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Q & A: True interchangeability of tool components

June 1, 1997

6 Min Read
Q & A: True interchangeability of tool components

Interchangeable core and cavity components are recognized as a way to provide value to the customer by helping maintain high levels of production and minimizing downtime. While nearly every moldmaker provides spares, there is a difference between spares and true interchangeability.

John Thirwell, vice president of marketing and sales for Caco Pacific in Covina, CA, says that it requires a completely different mindset about moldmaking to provide truly interchangeable cores and cavities.

Bill Kushmaul, CEO of Tech Mold Inc. in Tempe, AZ agrees. Although the term interchangeability is often heard among the moldmaking community, it isn't something that is necessarily important to every mold, and is generally used only with specific types of customers in certain markets.

Thirwell and Kushmaul recently discussed the concept of interchangeability and its importance in those markets with IMM.

IMM: What is the definition of interchangeability?

Kushmaul: In true interchangeability, you have a world where parts are parts. It used to be that when you provided spares for a mold, you provided a spare for cavity one, a spare for cavity two, a spare for cavity three, and so on. You could not use cavity one's spare in cavity three if cavity three went down because each one contained a minute tolerance difference.

Interchangeability means that you have spare core and cavity components that are so accurate in tolerances that it doesn't matter which spare replaces which core and cavity, or whether it's one mold or a hundred molds, it produces exactly the same part in all instances.

IMM: Why isn't interchangeability provided with every mold built?

Kushmaul: What interchangeability brings to the party is enormous, but only if a certain set of conditions exists. Interchangeability is crucial primarily for global projects involving an established product in which the manufacturer needs the highest possible quality at the lowest cost to manufacture in seeking to establish market dominance.

Thirwell: Some molded parts have wide tolerances because they are stand-alone components. They don't have to fit with other parts. Molding a letter opener has much different parameters than molding a computer keyboard, for example. There's no reason to spend the money necessary to make every letter opener's tolerance within tenths.

IMM: What are the implications of interchangeability in the global sense?

Kushmaul: It means that a customer with molding plants worldwide pumping out billions of parts - printer cartridge components, for example - can buy a mold, put it in any press anywhere in the world and make the exact same parts. If a core and cavity goes down in Asia and you're out of spares, you can borrow spares from the plant in Europe. You only need to certify the steel.

Thirwell: It makes having global operations much easier, and makes part quality in any location in the world controllable.

IMM: Can you tell us the importance of the "parts are parts" scenario to the customer?

Kushmaul: In many cases, the customer puts the plastic components through some type of automated, high-speed assembly or packaging equipment. This automated equipment is designed to handle parts with a specified tolerance, which means consistency in part dimensions is crucial to its use. Parts with varying dimensions can cause the assembly equipment to go down.

Thirwell: In the medical world, if parts are not identical there can be a health risk. Certain parts need to fit in blood analyzers and centrifuges. If there is variation within the parts that causes them not to fit properly - if they're not interchangeable - the parts can break in test and there's a high degree of contamination risk.

IMM: What do you think has driven the increased use of interchangeability?

Thirwell: Three things, really. First, molding automation. The use of robots when you want to take parts out of a mold requires that the robots grasp certain areas of the part, which means that all the parts have to be the same.

Second, the postmolding, added-value operations that are automated - such as printing, labeling, assembly, or anything else downstream from the molding machine - require a high degree of cavity-to-cavity likeness, otherwise nonconforming parts interfere with the automation processes.

Third, parts that eventually go to make an assembly of a multitude of parts have to be assembled with other parts that come from other cavities from many molds. High-speed assembly equipment is often used, and if all the parts aren't completely interchangeable, nonconforming parts cause jams in the automated equipment.

Kushmaul: In years past, we built molds using primarily manual labor and skilled craftsmen. We didn't have equipment that was accurate enough to produce the high-quality parts necessary to make interchangeability on a large scale possible. So offering that was a special thing done only rarely for certain customers.

IMM: How has that changed in the past five years?

Thirwell: In true interchangeability, there can be no hand or benching operations; no quick programming or hand finish operations can be tolerated. You must go to extremes in design and programming, and the inserts cannot be hand touched.

You must completely eliminate the human factor in production. Moldmakers will become only assemblers. They will take the part as it comes off the machine and assemble it into the mold. That's why only a handful of companies provide this service. It's costly and requires certain skills.

IMM: How has the use of automated machining and computer numeric controlled EDM, milling machines, etc. enhanced the availability and use of interchangeability?

Kushmaul: The equipment available now is so good that it plays a factor in making interchangeability a more standard practice. We don't need people with 40 years of experience to produce the components. We're trading in skills for better organization and program management. Precise machine tools require that you be better organized.

Thirwell: To provide interchangeability, you have to set up your engineering and design areas properly. It all starts with mold engineering, through extensive programming and then precision machining to produce inserts that are truly interchangeable.

CNC equipment can help tremendously, providing the CAD/CAM equipment is put to proper use and is programmed for interchangeability. Many moldmakers have CAD/CAM and CNC equipment, but they get it more for simplifying or speeding up operations, which is fine. But if the capabilities are optimized and programmed properly, then it's a tremendous help.

Kushmaul: The future of these automated machines - CNC jig grinders, CNC milling machines, and EDMs - will allow us even more interchangeability than in the past. But then you run into this problem of two worlds.

IMM: Explain what you mean by that.

Kushmaul: Currently, moldmaking is moving in two different directions at once. World one is faster, cheaper. At the other end of the spectrum you have world two, which is high quality, solids designing, and interchangeability, which are really offset by a world demand for quickness. At some point these two worlds will converge. Machinability and speed will come together, but right now there's a gap between quality and speed.

IMM: Are you saying that the technology to blend these two isn't available yet?

Kushmaul: The technology is there, it just hasn't been developed for the [moldmaking] industry. We need more extensive use of automation to achieve quality and speed.

IMM: What is the demand for moldmakers to provide true interchangeability?

Thirwell: Everyone that deals with high-end OEMs producing high-volume molds, especially for parts used in automated assemblies has to offer interchangeability because their customers demand it.

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