Purchasing Patterns: The Foundation of Castings
Anyone who sources cast components will at some point be faced with purchasing pattern equipment to produce the parts. Pattern equipment is expensive, produced in many different materials, and made up of several different components, all of which can be confusing.
Casting tooling often is more misunderstood by sourcing specialists than castings themselves. After all, a cast component is the end product you see when your order is completed. But with some basic information about patterns, you can understand how the equipment works and know how to purchase casting tooling.
Patterns are forms made of wood, plastic, metal or another material used to form sand molds to produce metal castings. Coreboxes are used to produce sand forms that are placed into a mold to produce an internal form or feature that cannot be produced by the pattern. Coreboxes also can be made of several different materials to meet the demand of the cast component.
Pattern equipment is no longer produced by hand on a bench using the traditional hand tools found in a cabinetmaker’s shop. It usually is designed using the casting end-user’s computer-generated solid model and constructed on large CNC machining centers. This giant step forward in the industry has led the way in reducing overall lead times and helped to eliminate human error in construction.
Why the Different Materials?
Pattern material selection is directly related to the frequency with which the equipment will be used. A pattern material exists for literally any part volume you require. For example, for single use or prototype runs, polystyrene can be used. Pine or another soft wood can be used for volumes that do not exceed 200 pieces per year; hardwoods are used when volumes approach 750 pieces annually. For annual volumes in excess of 750 pieces per year, patternmakers can use RenShape plastic. RenShape 5169 is a polyurethane board designed for machining extremely durable and wear resistant metalcasting patterns, coreboxes and other tools that require high impact resistance. These plastic materials can last up to several thousand cycles before requiring repair. When annual volumes exceed 5,000 pieces, metals such as aluminum or iron should be used. These patterns are the most expensive available but provide the longest life.
Managing Your Assets
Pattern management is not only the responsibility of the metalcaster. You should be in touch with the process, as well. As one of your company’s largest depreciating assets, tooling must be managed properly to control your costs. All pattern equipment, regardless of the material used to construct it, will require refurbishment and eventually replacement. Monitoring the volume of parts made from your tool will help in predicting refurbishment cycles and when the pattern must be replaced.
Make a point of reviewing your pattern equipment when visiting your metal casting supplier to audit its condition, how it is stored and how it is maintained. Regular upkeep of your pattern should fall under the responsibility of the metalcaster and should include general repairs of all the components.
Choosing a Pattern Source
It has long been customary for patterns to be purchased by the metal casting source. That trend continues, but today increasing numbers of OEMs are sourcing patterns themselves. While procuring your own tooling has its benefits, you must be careful when selecting a source for the equipment. Choose a reputable source that produces a quality product and is capable of working closely with your metalcaster. Independent sourcing does come with some risk, as you will be required to sort out dimensional and construction issues with the pattern manufacturer. Make sure you understand the pattern construction process before sourcing your own patterns.
Remember, quality metal castings start with quality pattern equipment.
--Bob Mueller Jr., P&H Mining Equipment, Milwaukee, Wisconsin
Bob Mueller Jr. is casting procurement specialist for mining equipment producer P&H Mining Equipment, Milwaukee. He has 23 years of casting experience.