Published 3/1/2009

Improving Quality and Lowering Mold Component Cost

Ejector and core pins come off the grinding machine with an SPI 4-5 surface finish when using special grinding process technology and proprietary diamond grinding wheels.

Jeffrey Smith

The Component Challenge and Solution

New grinding processes and CNC equipment produce close-tolerance repeatability. It is not uncommon to make 1,000 pieces of an ejector pin and have a total diameter tolerance variance of .00003-.00008. Flatness and parallelism for ejector blades is essential as is sleeve concentricity of .0004 or better.

The advent of computer-controlled heat treating of premium M-2 steel has greatly aided tool builders requiring .0937 diameters down to .004 diameter. Good surface finish and stable molecular structure allow three to six times greater wear resistance, and significantly reduce brittleness and breakage (see Photo).

Recent technology using special grinding processes and proprietary diamond grinding wheels, allow ejector and core pins to come right off the grinding machine with an SPI 4-5 surface finish. With this technology nearly 80 to 90 percent of polishing is eliminated, greatly reducing the component cost. Current sizes range from .500 diameter to 6" long.

Water-cooled custom core pins for medical and personal care products are manufactured with a standard 6-10 micro finish.

Strict adherence to .0002 shut-off heights and .002-.003 radii is critical. Total roundness and concentricity is maintained with Ded-Tru grinding operations. Typical syringe core pins with multiple diameters measure .0001-.0002 concentricity (see Photos).

Delivery Time Is Essential

When mold builders are looking for a component supplier, not enough can be said about the importance of on-time delivery. Often, $1,800.00 worth of custom core pins is the last component to be assembled in a $200,000.00 mold. Turning down work is not easy, but when a component supplier knowingly cannot meet the expected delivery schedule, communication becomes essential.

Unusually designed components also must be addressed at the time of quoting. Halfway into a job is no time to start asking for geometry or tolerance changes. Obvious mold repairs require quicker deliveries and completely accurate shipping information.

Because of reduced leadtimes for mold build and repair, moldmakers need to focus on readily available inventory—not only standard components, but specialty products, such as .001 increment core pins and +.0005, +.001, +.002, +.005 ejector pins.

In addition look for .0001 increment M-2 ejector/core pins with one-week delivery, which can save mold builders time and money in mold repairs. High inventory levels are difficult in the current economy, but component suppliers that maintain more than 400 different diameters in stock open the door to many options for tool builders.

Look for suppliers that have additional manufacturing support, which can expand their ability to offer size ranges to 36 inches for pins and .002 diameter to 1", as well as blades (13.5" long) and .010 thick with tolerances running .000080, which can expand a designer’s ability to create more technically challenging part configurations.

Summary

As the molding industries advance, the passion of perfection continues as component suppliers serve the most demanding component applications for high-cavitation mold builders.

Choosing the Right Component Supplier
Tech Mold, Inc. (Tempe, AZ) is a manufacturer of close-tolerance, high-cavitation, plastic injection molds that does most of its close tolerance machining in-house; however its core pin and sleeve work is outsourced because of the specialty equipment required.

When choosing a core pin and sleeve supplier, Tech Mold expects:

On-time delivery
Made to print specification (including steel type and hardness)
Quantity ordered is received (up to 10 percent over)
Sharp edges kept sharp
A #10 or better grind finish on non-molding features
A #8 or better grind finish on molding diameters (plus, these surfaces are to be free of grinding tears that create issues for stoning and polishing)
Diameters that mold plastic should be in the center of the tolerance (polishing stock allowance already figured in) due to CPK considerations
Fit diameters should be in the center to the low of the tolerance

Also because Tech Mold produces molds for nylon plastic parts, which are commonly known as having a critically small flash factor, another key to choosing the right component supplier, such as Smith Enterprises, is its ability to hold tight diameter tolerances.

In the past if Tech Mold wanted 80 pins for a mold, they would order 120 pins to find 80 within a .0001 window. With the right component supplier, they can order 80 and get 80 within the specified .0001 window. No grouping of pins is necessary.

Additionally, if Tech Mold needs pins that are stock catalog items from other vendors, they looked for a mold component supplier from whom they can order them as custom made, and which would be less expensive and closer tolerance.

Tech Mold does incoming inspection of all outside vendor items. The core pins and sleeves are manually inspected for roundness and some are super miked for size.

The vast majority of the inspection is done by Tech Mold’s Tesa Scan 50 Plus scanner machine.

The pin is placed in the machine and the first pin is scanned, which takes only seconds. The image of the pin then allows the operator to choose the diameters, radii and angles that need to be inspected for each subsequent pin. Using this parallel white light system allows Tech Mold to get the dimensional results within a .00005 window for all pins.

In today’s tight marketplace, Tech Mold has found that working with proven and reliable vendors has given them the ability to survive in the tough times.