Your money is in the mold - care for it

I recently attended a meeting of the local SPE chapter and we took a plant tour. As we walked through the facility everyone in our group noticed two large safe doors in parallel hallways. They appeared to be the entrance and exit to something highly secret. At the end of the tour we stopped in front of one of these massive steel doors, and with a wink our guide spun the handle and pulled it open.

     We walked into a mold storage facility. The vault doors served two purposes. The first was strictly advertising. It proved to customers (existing and potential) how valuable molds are and how much security and protection is provided for tools.

     The vault also acted as a firewall. Our guide explained that the walls consisted of metal studs and sheet rock, and the sheet rock used was unusually thick to make it more fire-resistant than code required. I looked at the ceiling. The owner caught my glance and said there was no fire extinguisher system in the vault. The room held only molds, and if there was a fire in the plant water spraying from the ceiling could ruin the tooling. Additionally, the vault was dehumidified to inhibit rust.

Protect Your Assets
This concept of a factory that contains one room devoid of fire extinguishing capabilities required much explanation to the city fathers, the zoning folks, and ultimately the fire department, but it makes awfully good sense. Molding machines can be repaired and up and running quickly. But consider this: Many molders handle as many as 500 active molds; if they all took a bath in an extinguisher system and received a thorough rinsing from the fire department, the damage to production would be catastrophic.

     Most molders store tools on shelves either in the molding department or off in a corner of the plant. But some smart molders have built separate cinder block buildings to store molds. This is worth considering.

     Of course, just because you've stored your molds well doesn't exempt you from risk and damage. It never fails to surprise me that folks understand the need to change the oil in their car, tune up the engine, and rotate the tires, but will only work on a mold when it breaks.

How to Cope
Molds wear out for a variety of reasons. One of the simplest things to avoid is rust. When steel, oxygen, and water get together the chemical reaction is rust. While we can debate if rust is a problem elsewhere in the mold, no one will dispute that a rusted cavity is a problem.

     This can be avoided in at least three ways. First, never pull the mold cool. Open it and heat it with the waterlines. This drives off condensation. Second, always use a mold preservative. If the mold is dry when you spray it, it will stay dry. If the mold surface is wet when you spray it, you'll get rust. Third, blow out the waterlines. While many people debate the merits of waterline hygiene, the real purpose is to ensure that when the mold is put on the rack it doesn't drip water onto another mold or leak into its own parting line.

     Mold wear is also caused by abrasive resins. While tool steel is hard, fillers or high-heat crystalline materials erode steel the same way water polishes a granite pebble in a stream. Because we have to inject the plastic into the mold, this is merely the cost of doing business. The best way to cope with this is to check for washout near gates and sharp corners. When this occurs the mold must be fixed.

Kinder, Gentler Processing
The number one preventable cause of premature mold wear is abusive processing. Overclamping the tool causes hardening at the parting line that eventually chips the steel. Leaving bits of flash on the mold face hobs into the mold, eroding the clamping surface. Allowing rust to accumulate on outside clamping surfaces forces the mold to be out of parallel. This abuse is temptingly (temporarily) solved by overclamping.

      There are still other abuses: Blocking gates, or turning off sections of the hot runner system to block a gate, distorts the distribution of pressure in the mold. While steel does have an elasticity, over time the process will deteriorate. A minor problem is the well-intentioned but ill-equipped molding technician who pulls out stuck sprues and gates with heated steel screws, or digs out stuck parts with pliers and chisels. This scratches, dings, and dents the tool, instigating repairs.

     Unfortunately (and this must be explained to your customer) the highest cost of maintenance and wear is unreasonable and unnecessary specifications. High-tolerance tools, those with high CpKs, have frequent part inspections and corrections.

Most molders babysit high-tolerance parts by adjusting and tweaking process conditions and by blocking cavities. A quick look at the economics of this scenario, however, proves that you are better off shipping hundred dollar bills to your customer than you are shipping product.

     If you have a choice, always go for the tooling change and not the process change. Educate your customers. Use industry standards. If you can't argue for good parts based on dimensions, set up a functional testing protocol that avoids argument over a thousandth of an inch.

     Unfortunately, molds of low-volume parts, or parts that are about to be obsoleted, are usually not maintained. The justification for maintenance is easier when you are shipping millions as opposed to hundreds. However, the margins on high-volume parts are usually small. The cost of maintenance over a small run usually means you are losing money.

     Communicate to the customer what your maintenance policy is, specifying who pays for it and when it will occur. If the customer expects it in the part price, readjust the price. If the customer won't pay for maintenance, explain the consequences of his philosophy and either hope for the best or return the tool.

     My mission statement is simple: All blessings flow from the shipping dock. You can't put good parts on the dock without good tooling. You can't make a profit if you run blocked cavities, bad tooling, and slow cycles. It would be nice if I never had to maintain my car, but I do, and it runs like a dream.