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Use of Altshuller’s Matrix for Solving Slag Problems Related to Steering Knuckle (Part I of II)

| On 15, Mar 2002

Use of Altshuller’s Matrix for Solving Slag Problems Related to Steering Knuckle (Part I of II)

TRIZ case study in the process industry

Edgardo CORDOVA LOPEZ
INSTITUT NATIONAL POLYTECHNIQUE DE TOULOUSE-ENSIACET
Laboratoire de Génie chimique, UMR-CNRS 5503
Edgardo.CordovaLopez@ensigct.fr
INPT tel. (+33) 05 62 88 58 42, fax 05 62 88 57 85

Germain LACOSTE
Directeur de l’ECOLE NATIONALE D’INGENIEURS DE TARBES
Laboratoire de Génie Chimique, UMR-CNRS 5503
Germain.Lacoste@enit.fr
ENIT Tel. (+33) 05 62 44 27 01, fax (+33) 05 62 44 27 27

Jean-Marc LE LANN
JeanMarc.LeLann@ensigct.fr
Responsable du Département Genie Industriel
Laboratoire de Génie Chimique, UMR-CNRS 5503
ECOLE NATIONALE SUPERIEURE DES INGENIEURS EN ARTS CHIMIQUES ET
TECHNOLOGIQUES (INPT-ENSIACET)
ENSIACET tel. (+33) 05 62 88 58 33, fax (+33) 05 62 88 57 85

ABSTRACT

Volkswagen of Mexico S.A. de C.V, the well-known german automotive industry has become the first company in Mexico and perhaps in Latin America using the TRIZ methodology in order to improve its processes of production. The line of foundry manufacture for one of its pieces of safety, namely the steering knuckle, has presented from the beginning various quality and operation problems. It is a strategic piece for the security of the passengers in cars since it is closely interacting with the direction, the shock absorbers, and with the front wheels. Two great problems have been accurately identified: one is the slag and the other one is referring to the sand system for the manufacture of molds. The matrix of Altshuller, a key milestone in the TRIZ methodology for innovation technology has allowed to help for proposals of valuable and sustainable solutions to solve these great problems that originate scrap causes, such as “solidification shrinkage”, “sand rain” or “ porosity”. All of these cause a high percentage of scraps or reworks. In this paper, the first of them, namely the slag problem will be analyzed.

Key words: TRIZ methodology, steering knuckle, contradictions, ideal solution, Altshuller’s matrix, Inventing principles, slag

1. INTRODUCTION

TRIZ is a new methodology born in Russia (called Theory of Inventive Problem Solving). TRIZ is a knowledge-based technology for speed-up development of design concepts. The power of this methodology is based in the evolution of successful products, ways to overcome psychological barriers, and generalization of the ways used to solve several problems in the most innovative inventions. TRIZ is able to analyze products or process functions in order to best use its resources and identify the best opportunities for its development. Many papers about TRIZ have been published in difference international revues, the most important and dedicated is the triz-journal. ( www.triz-journal.com ) [4]

1.1 Overview of the Company.

The Volkswagen firm in Mexico is one of the most important automotive industries around the country. It is conformed to a great amount of industrial ships and various processes of production that conform everything in an industrial system that makes the manufacture possible of the different automobiles which, at the present time, are sold in the country. The macro-industry of more than 15000 workers has just produced its unit number 5 million in more than 30 years of existence. It uses the most modern methods of production and the most advanced management quality systems. It is located in Puebla next to mountains and only 80 miles from Mexico City. [1]

1.2 The Piece.

The steering knuckle is an important part of the vehicle that allows fixing the front wheel brakes, the motion of direction, the fixation of the shock absorber, and the axis of impulsion. This piece is of safety importance whereas it is subject to diverse types of strengths in different directions and must strictly fulfill the design-required parameters. (Fig.1)

1.3

The Material

This piece is made with ductile iron. After a magnesium-based reaction, the iron is impregnated with a large amount of nodules that present, at the microscopic level, the appearance of spherical bubbles. These particularities allow for ductility and resistance to the tensions. It induces an extraordinary resistance to the breakage and/or the flexion. For that reason, it is necessary in this process of reaction to introduce certain substances such as carbon, silicon and others in order to give the required properties to the piece. [1]

1.4 The Process.

The production in the foundry manufacturing line begins with the induction furnaces that are fed mainly with new raw material, recycled material, and scrap pieces. These furnaces melt and mix the material with other necessary substances for the casting process (temperature>1400°C). Later, the iron-base is put under a reaction process using magnesium in order to form nodules that allow it to acquire certain physical properties of ductility. It allows for the manufacturing of a piece whose function is associated to diverse efforts and tensions that cause their critical parameters and its meticulous control. Then the casting process is performed. A casting is a metal part formed by pouring molten metal into a sand mold. The mold is composed with two halves that form a cavity into which the molten metal is poured. The mold forms the external surface of the casting. If an internal cavity is required in the casting, a core is placed inside the mold cavity, as in the case for our piece.

After the metal solidifies, the mold is broken, the core removed and the part is ready for finishing operations. The sand is then remolded, prepared and used again in a cyclic process.

Then, there is a cooling process that strips the two pieces which are then drained: a right and a left one, totally symmetrical that separated by a ‘branch’ that serves as a joint between both pieces (which is known as recycled or returned material). At the same time, the sand is recovered in order to be reused through a transportation band until the sand tower, where the sand has already been treated with water in order to fulfill the required humidity. Some pre-mixed substances that give the sand agglutinates properties have also been added. The pieces, cold and clean, are tested in laboratories in order to avoid out of specification pieces, arriving at the machine process. Finally the pieces are re-assembled.

1.5 The Basic Problem.

The manufacturing line in its first foundry step for the steering knuckle has been recently started. It was implemented less than a year ago and since then a lot of problems have had to be surpassed, reflected in the high percentage of scraps and reworks considerably increasing the operating costs. The main causes of these scraps are the ‘solidification shrinkage’, that is a deformation of the piece because of the metal in fusion does not fill the mold in certain points due to a premature cooling. The ‘sand rain’ attributed to that the molds do not have the properties with required humidity or agglutination and thus they are deformed at the moment of the casting. In addition to these two reasons that cause 90 % of scraps, there are also the porosity, the struck piece, and others which causes are attributed to diverse reasons. Nevertheless, most of those problems may be eliminated or diminished if two great fundamental problems can be solved: the slag and the recycle sand quality.

The excess of sand deposited in the hopper feeding the induction furnaces, impregnated in the return material is certainly the main cause. Using the Altshuller’s matrix we will able to analyze these two great problems and we will try to propose a solution for each of them. In this paper we will analyze only the first problem.

2. ANALYSIS OF THE PROBLEM

The slag is one of the most persistent problems; it is the impurities that are detected in the metal before the casting process. This problem is originated mainly in the material of return or the scrap pieces that are impregnated with an important amount of sand, as product of strips, which cannot be easily eliminated. The slag represents a contaminant element that is necessary to eliminate or to diminish before the casting process to avoid scraps. From the point of view of the Altshuller’s matrix, we want to improve the adaptability of the metal, since the slag causes the metal to not fulfill the desired conditions for fluidity. Nevertheless, the main challenge is the natural effect of the high temperature and conditions of the process that prevent or make difficult any effective remedial action. The ideal solution is that the scrap pieces or the material of return do not contain sand at all [5], but it is a difficult task by the inherent conditions of the process. If we consulted the Altshuller’s matrix in line 35 related to Adaptability and column 17 referring to Temperature, we find the numbers 2, 27, 3, 35 that correspond to the inventive principles suggested by the matrix. (The matrix can be consulted and used in http://www.inp.nsk.su/~dolgash/triz/index.html ). Each of them has been analyzed carefully in order to give the right answers.

Inventive principle 2. Taking out

A. Separate an interfering part or property from an object, or single out the only necessary part (or property) of an object.

  • Locate a noisy compressor outside the building where compressed air is used.

  • Use fiber optics or a light pipe to separate the hot light source from the location where light is needed.

  • Use the sound of a barking dog, without the dog, as a burglar alarm. [2]

  • Interpretation: The separation of the polluting elements that are accumulated in the superior part of the hoppers (Slag) must make with some special devices in the same way one takes off the cream from a glass of milk. This solution is in fact already practiced each day in order to controlling the excess of slag. Although it is only a partial fix and it does not represent a solution to the problem.

    Inventive principle 27. Cheap short-living objects

    A. Replace an expensive object with a multiple of inexpensive objects, comprising certain qualities (such as service life, for instance).

  • Use disposable paper objects to avoid the cost of cleaning and storing durable objects. Plastic cups in motels, disposable diapers many kinds of medical supplies. [2]

  • Interpretation: the addition of some components could neutralize the injurious effect of the slag, for example the use of salts or saline solutions that have a neutralizer effect and make easier the operation of extraction. This method is already considered and practiced in a regular way within the process, obtaining a significant decreasing of the problem.

    Inventive Principle 3. Local quality

    A. Change an object’s structure from uniform to non-uniform, change an external environment (or external influence) from uniform to non-uniform.

  • Use a temperature, density, or pressure gradient instead of constant temperature, density or pressure.

  • B. Make each part of an object function in conditions most suitable for its operation.

  • Lunch box with special compartments for hot and cold solid foods and for liquids

  • C. Make each part of an object fulfil a different and useful function.

  • Pencil with eraser

  • Hammer with nail puller

  • Multi-function tool that scales fish, acts as a pliers, a wire stripper, a flat-blade screwdriver, a Phillips screwdriver, manicure set, etc. [2]

  • Interpretation. This principle suggests to avoid that the sand arrives at the furnaces or at least, it does not arrive in excess or, if it arrives that some reaction process is possible in order that the slag becomes operational or its effect is unnoticed.

    Perhaps to obtain some external agent allows avoiding the excess of sand in the furnaces.
    This problem will be analyzed in section 3 like one more contradiction.

    Inventive principle 35. Parameter changes

    A. Change an object’s physical state (e.g. to a gas, liquid, or solid).

  • Freeze the liquid centers of filled candies, then dip in melted chocolate, instead of handling the messy, gooey, hot liquid.

  • Transport oxygen or nitrogen or petroleum gas as a liquid, instead of a gas, to reduce volume.

  • B. Change the concentration or consistency.

  • Liquid hand soap is concentrated and more viscous than bar soap at the point of use, making it easier to dispense in the correct amount and more sanitary when shared by several people. [2]

  • C. Change the degree of flexibility.

  • Use adjustable dampers to reduce the noise of parts falling into a container by restricting the motion of the walls of the container.

  • Vulcanize rubber to change its flexibility and durability.

  • D. Change the temperature.

  • Raise the temperature above the Curie point to change a ferromagnetic substance to a paramagnetic substance.

  • Raise the temperature of food to cook it. (Changes taste, aroma, texture, chemical properties, etc.)

  • Lower the temperature of medical specimens to preserve them for later analysis. [2]

  • Interpretation. To make the undesired material become more evident and manipulable in order to eliminate it more easily. To use the effect of some chemical reaction to cause all the impurities that cause problems to ascend to the surface and make its recovery easier. This operation would be unnecessary if we managed to avoid that the sand arrives at the furnaces in excess.

    3. ANALYSIS OF THE PROBLEM OF THE NON-ADHERED SAND ON

    THE RECYCLED MATERIAL

    Since the problem of the slag is mainly attributed to the high sand content, the problem must be presented in such a way that the possibility that the sand arrives at the furnaces does not exist or it arrives only with a minimal amount. The recycled material as well as the scrap pieces are transported in freight elevators that in addition to the material cannot avoid to transport a great amount of sand non-adhering to the material. Let us say that the sand adhered to the material will require other methods of solution (section 4), but it is possible to avoid that the loose sand arrives at the storage zone of the recovery pieces, making it very difficult to eliminate without increasing the cost of the processing. Therefore, the following situation exists: we would like to eliminate the undesired material during the transport process but the amount of material to transport prevents it; that is to say, the parameters are: line 33, Ease of operation and column 1, Weight of a Mobil object. The precognized inventive principles suggested by the matrix are: 25, 2, 13 and 15. Let us analyze carefully these principles and try to find answers adapted to our problem.

    Inventive principle 25. Self-service

    A. Make an object serve itself by performing auxiliary helpful functions

    • A soda fountain pump that runs on the pressure of the carbon dioxide that is used to “fizz” the drinks. This assures that drinks will not be flat, and eliminates the need for sensors.

    • Halogen lamps regenerate the filament during use–evaporated material is redeposited.

    • To weld steel to aluminum, create an interface from alternating thin strips of the 2 materials. Cold weld the surface into a single unit with steel on one face and copper on the other, then use normal welding techniques to attach the steel object to the interface, and the interface to the aluminum. (This concept also has elements of Principle 24, Intermediary, and Principle 4, Asymmetry.)

    B. Use waste resources, energy, or substances.

    • Use heat from a process to generate electricity: “Co-generation”.

    • Use animal waste as fertilizer.

    • Use food and lawn waste to create compost. [2]

    Interpretation in the context of our problem: The freight elevator must clean the return material during the transportation; that is to say, not only should it transport but also it should be able to clean it. This can be performed through some device of suction (aspiration) using its own calorific or electric power energy to avoid extra costs.

    Inventive principle 2. Taking out

    A. Separate an interfering part or property from an object, or single out the only necessary part (or property) of an object.

  • Locate a noisy compressor outside the building where compressed air is used.

  • Use fiber optics or a light pipe to separate the hot light source from the location where light is needed.

  • Use the sound of a barking dog, without the dog, as a burglar alarm. [2]

  • Interpretation: The extraction of the sand is confirmed with this principle as it was settled in the previous principle.

    Inventive principle 13. ‘The other way round’

    A. Invert the action(s) used to solve the problem (e.g. instead of cooling an object, heat it).

  • To loosen stuck parts, cool the inner part instead of heating the outer part.

  • Bring the mountain to Mohammed, instead of bringing Mohammed to the mountain.

  • B. Make movable parts (or the external environment) fixed, and fixed parts movable).

  • Rotate the part instead of the tool.

  • Moving sidewalk with standing people

  • Treadmill (for walking or running in place)

  • C. Turn the object (or process) ‘upside down’.

  • Turn an assembly upside down to insert fasteners (especially screws).

  • Empty grain from containers (ship or railroad) by inverting them. [2]

  • Interpretation: This principle suggests to undo the leftover sand before the material is unloaded and not later, inverting the deposit, previously covered by a very resistant mesh that can load all the material, so that only the sand drains. Later the material without the protective mesh could be unloaded in the corresponding area.

    Inventive principle 15. Dynamics

    A. Allow (or design) the characteristics of an object, external environment, or process to change to be optimal or to find an optimal operating condition.

  • Adjustable steering wheel (or seat, or back support, or mirror position…)

  • B. Divide an object into parts capable of movement relative to each other.

  • The “butterfly” computer keyboard, (also demonstrates Principle 7, “Nested doll”.)

  • C. If an object (or process) is rigid or inflexible, make it movable or adaptive.

  • The flexible boroscope for examining engines

  • The flexible sigmoidoscope, for medical examination [2]

  • Interpretation:

    A double bottom of the return material deposit could be a good solution.

    The first bottom is a solid surface with innumerable perforations so that the sand filters to a second bottom.

    Once this has happened, a sliding device will cause the perforations to be obstructed so that to the deposited, material created by inverting, the sand remains intercepted between the two bottoms of the deposit.

    A system of aspiration using the same energy of the freight elevator (calorific, mechanical or electrical) will drain the sand content to the corresponding area or, by inverting. (Fig.2)

    Fig.2 Deposit of return material with double bottom

    4. ANALYSIS OF THE PROBLEM OF THE ADHERED SAND ON THE RECYCLED MATERIAL

    The problem of the adhered sand to the return material is one of most seriousness. There is not a method that allows eliminating the sand that contaminates the induction furnaces and therefore, increases the amount of slag that prevents the process as a whole.

    The ideal solution would be that the premix* that is added to the sand had the property to maintain in hot conditions its properties of adhesion or agglutination but in cold conditions, these properties were lost. As this solution is not sustainable (that rather corresponds to the sand supplier), it will be necessary to consider other solutions. We will settle this problem like a contradiction of the following way: What we want is to clean to the surface of a movable object that is the material that is transferred to the recovery area. Nevertheless, a resistance exists because the sand is compacted to the material and therefore the cleaning work becomes difficult.

    Consulting the Altshuller’s matrix, in line 18 (Brightness) and in column 14 (Strength) we find the numbers 35 and 19 as the inventive principles to be applied to solve this problem.
    Let us analyze each of them.

    Inventive principle 35. Parameter changes

    A. Change an object’s physical state (e.g. to a gas, liquid, or solid).

  • Freeze the liquid centers of filled candies, then dip in melted chocolate, instead of handling the messy, gooey, hot liquid.

  • Transport oxygen or nitrogen or petroleum gas as a liquid, instead of a gas, to reduce volume.

  • B. Change the concentration or consistency.

  • Liquid hand soap is concentrated and more viscous than bar soap at the point of use, making it easier to dispense in the correct amount and more sanitary when shared by several people.

  • C. Change the degree of flexibility.

  • Use adjustable dampers to reduce the noise of parts falling into a container by restricting the motion of the walls of the container.

  • Vulcanize rubber to change its flexibility and durability.

  • D. Change the temperature.

  • Raise the temperature above the Curie point to change a ferromagnetic substance to a paramagnetic substance.

  • Raise the temperature of food to cook it. (Changes taste, aroma, texture, chemical properties, etc.)

  • Lower the temperature of medical specimens to preserve them for later analysis [2]

  • Interpretation: this principle suggests to react the sand adhered to the material, submerging it in an acid or an alkaline liquid of a certain concentration so when reacting, the sand becomes loose. Exactly like it happens with grease when reacting it with liquid stove cleaner, this acquires a favorable consistency for its cleaning without affecting the surface of the material. This operation can be conducted by those who make the separation of the pieces with the call “ branch” (material of return) without wasting a lot of time or effort.

    Inventive principle 19. Periodic action

    A. Instead of continuous action, use periodic or pulsating actions.

  • Hitting something repeatedly with a hammer

  • Replace a continuous siren with a pulsed sound.

  • B. If an action is already periodic, change the periodic magnitude or frequency.

  • Use Frequency Modulation to convey information, instead of Morse code.

  • Replace a continuous siren with sound that changes amplitude and frequency.

  • C. Use pauses between impulses to perform a different action.

  • In cardio-pulmonary respiration (CPR) breathe after every 5 chest compressions. [2]

  • Interpretation: this principle is complemented with the previous one, because once the cleaning liquid has been applied to the material, a movement of oscillation or periodic impulses can be applied to the deposit in order that the return material is undone of the sand that previously has been treated. These impulses can be made in a more efficient way during their transfer using the same energy the freight elevator does. The sand can be eliminated by suction or by inverting the deposit with a mesh that it prevents the material from falling. This solution is similar to the proposal for the loosened sand, therefore, the two could be conjugated and consequently any type of sand, either the released or the adhered one, does not arrive.

    Fig.3 The hopper with the perforation and the sand collector

    5. CONCLUSIONS

    The least expensive and fastest solution to implement is to make an extraction by inverting the deposit, holding onto the pieces by using a resistant mesh to unload the excess of sand. Although the most efficient solution is to use the deposit with a bottom, which has multiple perforations, so the sand falls into a second bottom to be inhaled or drained in a later operation to discharge the material. This solution implies an adaptation to the deposits of the material. If the ideal solution cannot be reached, the amount of slag could at least be reduced in a high percentage that is generated for sand reasons. A complementary action to assure minimum sand in the induction furnaces that also can operate in case that the previous operations are not possible is as follows: To modify the hopper that spills the material to the furnaces adding a great amount of circular perforations in the base of the hopper. At the moment it has only these perforations in a small area that is not sufficient to collect all the sand that already is loosened in the hopper. Thus, once the scraps or return material is deposited in the hopper, this one will be vibrated in order to obtain an effect of sifting and eliminate portions of sand, a sand collector will be adapted (see fig 3 and 4). This solution has been recommended and implemented with excellent results and without investment managing to reduce the scraps and reworks pieces from more than 10% to less than 3%.

    This demonstrates how using TRIZ methodology is interesting and how applying these concepts up to the revamping of a manufacturing chemical process may lead to significant improvements.

    It also demonstrates how a based theory approach may be efficient for help and may be used in manufacturing industry in order to improve end-user product, process, and processing.

    6. BIBLIOGRAPHY

    [1] Gerhard Schreiber. Eine Geschichte Ohne Ende. A Never-Ending Story. una historia sin fin. First edition 1998. Volkswagen de Mexico, S.A. de C.V.

    [2] Format for the 40 Inventive Principles and the accompanying examples, developed by Karen Tate and Ellen D. http://www.triz-journal.com/archives/1997/07/b/index.html
    [3] Zinovy Royzen, http://www.trizconsulting.com/ Case Study: TRIZ Solves a Hard Drive Reliability Problem
    [4] Terninko, John/Zusman, Alla/Zlotin, Boris Step-by-step TRIZ, Creating Innovating solution Concepts
    3th edition, 1996/responsible Management Inc. Nottinham, New Hampshire
    [5] Altshuller, Genrich. And suddenly the inventor Appeared, TRIZ, The Theory of inventive problem solving/ 2nd edition, published by Technical Innovation Center, Inc Worcester, MA/ 1996
    [6] V. Souchkov 1996/ Cav 1997 /K Tate/E. Domb, 1997 V. Souchkov 1996 http://www.triz-journal.com
    [7] Córdova-López, Edgardo/ TRIZ: Une manière innovante de résoudre les problèmes d’Ingénierie/ Mémoire presented on sept 10th. 1999 in the Institut National Polytechnique de Toulouse, Francia.
    [8] KOWALICK, James TRIZ-Journal, Nov. 1996, ( http://www.triz-journal.com )
    17 Secrets of an Inventive Mind : How to conceive World Class Products Rapidly Using TRIZ and Other Leading Edge Tools
    [9] KOWALICK, James TRIZ-Journal, Juin1998, ( http://www.triz-journal.com )
    TRIADS : Their Relationship to TRIZ. Elaboration on the Use of Triads and TRIZ solve Impossible Problems and Creat Next-Generation, Breakthrough Desings.

    [10] LEONCIO Jiménez Candia TRIZ-Journal, Nov/01 ( http://www.triz-journal.com )
    The Altshuller’s Contradiction Matrix in the Knowledge Creation of Innovation Case Study : The Honda City/ Institut National Polytechnique de Toulouse – France http://www.triz-journal.com/archives/1997/07/b/index.html

    __________

    Endnotes

    1. Correspondance to whom should be adressed
    2. Correspondance to whom should be adressed

    * the premix is elaborated with different adhesive substances like sodium and calcium benzonites, and carbon in order to give at the sand some adhesion proprieties.