Steel Selection-Closing the Gap with Offshore Tooling

To be competitive, domestic mold builders need to consider that steel selection-although the smallest portion of the overall mold manufacturing cost-can be a vital component in competing against cheap offshore tooling.

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The most discussed topic in the mold building industry today is cheaper tooling from offshore competition. Most often these discussions revolve around unfair low labor costs; however, many mold builders fail to realize that steel selection can play a major role in closing the price gap with offshore tooling.

Too often, moldmakers only look at the cheapest price-per-pound steel and ignore the real savings opportunities available above the waterline labor costs.

Steels that machine faster, achieve superior machine finishes to reduce bench time, weld better to ease design change or repair, do not require costly time off the machine for stress relieving and offer real labor (cost) savings. Fewer labor hours also mean improved leadtimes.

 

Real Tool Costs from Low Labor Cost Countries

Offshore tooling buyers focus on initial acquisition costs that are often well below half of the domestic quotes. These extremely low prices tend to come from Southeast Asian countries and China where labor costs are extremely low. The buyers are willing to ship the tool to a North American shop to bring it to operational specifications. There often are problems caused by miscommunication, lack of attention to detail or ignored specifications by the offshore shop.

One molder asked what grade of steel was used on his recently received tool. The reply from the Chinese tool builder was "yes". However, these buyers of offshore tooling are willing to accept the additional costs. They believe that even if the additional costs double the original acquisition price, they still saved money. They fail to take into consideration the below waterline costs. If the domestic shops can get closer to the initial offshore price, built-in advantages below the waterline, such as language, geography and quality will help to recapture lost business.

 

Lower Cost Tooling from Higher Labor Cost Countries

Japan is another story. Japanese labor costs are now higher than ours. Japanese moldmakers build tools quicker and cheaper than we do-and make a profit. But how? The answer is in steel selection.

The earliest molds in both countries were made out of boilerplate-or whatever carbon steel was available. As resins advanced and production runs got longer, changes in the steels used were required. North American shops went to chrome moly steels that could be heat treated-first 4140, then the more highly refined P-20 (4130 modified pre-hardened to HRC 26/32) and finally hardened tool steels such as A-2, H13 and S-7. Each step was made to extend the life of the tool, but at the expense of machinability, production time, repairability or required heat treatment.

Through the 1950s and 1960s, the Japanese zeroed in on JIS (Japanese Industrial Standard) S55C as its core and cavity steel of choice. S55c is a 0.55 carbon steel supplied at a brinnell hardness of 220. They valued ease of machinability and the corresponding timesavings as well as ease of repairability over hardness. Adhering to strict preventive maintenance allowed the molders to successfully complete their production runs.

As the Japanese electronics and automobile industries began to ramp up, it became apparent that harder, longer-wearing, pre-hardened steels would be required due to ever-increasing volumes. But the tool builders resisted any change that would add to mold building leadtime and the molders resisted any change that would make repair or modification more difficult. It became incumbent upon the Japanese specialty steel manufacturers to design steel grades that would satisfy both the mold builders and molders.

 

Chart 1

  JIS AISI SUPPLIED HRC DAIDO STEEL AICHI NIPPON KOSHUHA MITSUBISHI STEEL KOBE STEEL SUMOTOMO SANYO
CARBON STEEL 555c 1055 BHN220 PXZ AUK11 KPMI MT50C KTSM21 SD17 -
CHROME MOLY QUENCH AND TEMPERED STEELS P-20 MODIFIED SCM440 4140 HRC 30-33 PX5 AUK11 KPM2 - KTSM3M SD16 -
AGE HARDENING STEELS P21 MODIFIED - - HRC 37.42 *NAK55
*NAK80
-11 KAP *M524M KTSM403F *SHS100 PLM40
*VACUUM ARC REMELTED

Beginning with Daido Steel's 1965 introduction of a steel grade named NAK80, followed by NAK55-a re-sulphurized version in 1975-and PX5-a low carbon-improved P-20 in 1989-that's exactly what they did (See Chart 1). Each mill marketed its own variation under proprietary trade names of steels designed to keep labor time and cost low for the moldmakers and repair costs low for the molders. None of these grades were, or are now, identified by JIS or AISI standard designations. They are sold under the producing mill's trade name, but as a group they are the dominant pre-hardened cavity and core steels used in Japan.

 

How Paying More for Steel Reduces Mold Building Costs

Reduced machining time reduces leadtime, lowers labor costs and improves machine use. You can build more tools in less time, increasing revenues. Hunt Machine (Tallmadge, OH), a leading manufacturer of molds for the plastic, rubber and wood fiber industries, experienced what the modified P-21 grades could do to machining time first-hand. Vice President Dave Hunt discusses a tool cost analysis he was asked to do in 1992 for the then Inland Fisher Guide Division of G.M.

"The G.M. engineers were interested in NAK 55 for steering wheel molds because they could weld repair textured areas, re-texture and see no indication of a weld on the molded part. But they were concerned about the cost effect of switching to a $4.00 per pound steel for these eight hundred-pound molds. They came to Hunt Machine because we had built many of these tools out of P-20. We knew what we were doing and built the P-20 tools as fast or faster than anyone could. We built two tools of very similar geometry. We used the same 25 hp twin spindle machining centers, and our best combinations of carbide, indexable carbide, ceramic and HSS milling tools. We were confident that our results would be an accurate comparison within 10 percent. We found that the feedrates were consistently better with the NAK material and due to the stability of the age-hardened steel, we could eliminate the dead passes caused by the tool spring of P-20. We machined the NAK tool in 115 hours-less time than the P-20 tool. With our shop rates at the time it was less expensive to build the tool out of the $4.00 per pound steel," Hunt explains. "With today's improved machining and cutting tool technology, the qualities of these steels stand out even more."

This was proved out in a machining demonstration conducted by Makino in 1999. Two Makino waves were machined-one out of P-20 and one from a modified, low carbon PX series from Japan. Total machining time for P-20 was 3 hours and 59 minutes; machining time for PX5 was 2 hours and 57 minutes (See machining data in Figure 1a and 1b).

 

Figure 1a Makino Wave: Test Cut Report-PX5

Toolpath Cutter Coating RPM IN/M Chip Load Time
Roughing 3/4" ball end mill TiCN 9,600 236 .012 56 min.
Semi-Finishing 1/2" ball end mill TiCN 14,000 315 .011 21 min.
Finishing 1/4" ball end mill TiCN 18,000 228 .006 100 min.
Total Machining Time: 2 Hours 57 Minutes

 

Figure 1b Makino Wave: Test Cut Report-P-20

Toolpath Cutter Coating RPM MM/M Chip Load Time
Roughing 50 mm face mill TiCN 1,600 1176 .183 16 min.
Roughing 16 mm ball end mill TiCN 6,000 3000 .250 91 min.
Semi-Finishing 12 mm ball end mill TiCN 10,000 6800 .340 32 min.
Finishing 6 mm ball end mill TiCN 18,000 6732 .187 100 min.
Total Machining Time: 3 Hours 59 Minutes

 

Also stated in the Makino report was "The machining characteristics of the PX5 material compared to P-20 allowed for higher rpm and a much higher chip load for roughing and semi-finishing. The surface finish of PX5 is much better than P-20 even when only using air instead of liquid coolant."

Superior machine finish reduces or eliminates bench preparation for further processes. In the compression rubber mold industry, o-ring manufacturers have eliminated the need to polish o-ring cavities because of the machined finish they could obtain with the 40HRC P-21 modified steel. After the Makino demonstration one of Makino's engineers was asked why he had polished the PX5 wave and not the P-20 wave-neither had been polished.

Benching represents labor hours and additional costs. U.S shops are striving to use machined finished cores. They are striving to get a machine finish that will allow them to go directly to texture without benching. In Japan, this has been common practice for years. Takashi Matsuoka, president of Matsuoka Special Steel Co. Ltd.-a leader in steel distribution as well as semi-finished cores and cavities for large, automotive molds-and president of Shippo Molds-specializing in die cast and plastic injection molds in Nagoya, Japan stated the following, "Without the proper steel, it would be very difficult for us to supply the leadtime and quality that our customers expect from us. We cannot lose time due to wide variations in hardness-even in the largest blocks used for bumper molds. We view the added hand finishing this causes as additional cost to be avoided. Hard spots would be equally destructive to our labor and cutting insert budgets. We depend on unattended machining to keep our costs down. Cutters breaking on hard spots is not acceptable. The cutters we use for high-speed finishing cannot tolerate hard spots."

Larry Taylor, vice president of technical services for Complete Surface Technologies, Inc. (Rockford, MI)-a national leader in texturing, polishing, grain repair and benching-agrees, "It has been our experience that the uniform hardness supplied by these Japanese steels does greatly reduce benching time. When a technician has to change techniques due to hardness variations in the same block of steel, the hours can really start to add up. These steels have proven to be more uniform in their properties. You really see outstanding performance when they have been welded. The heat-affected zones (HAZ) stay close to the base metal hardness when properly welded and that really cuts down on the handwork."

 

Importance of Weldability to the Tool Builder and Molder

Design changes during tool construction are a fact of life. If the change takes place after texturing or polishing, the tool builder may have to start over. Welding on high carbon steels can cause a dramatic rise in hardness in the area adjoining the welded area-called the heat-affected zone (HAZ). If this hardness cannot be drawn back to a reasonable level (often it cannot), it is very difficult to match the texture or polish to the rest of the tool.

Dave Hunt recalls an early G.M. horn pad mold built from P-21 modified variation NAK 55. After the textured mold had been completed, designers relocated the bugles. Dave recalls the project engineer at the time, Paul Byran, stating, "If we cut the cavity out of P-20, we would have had to start over." Pete Ruggirello, executive vice president of Complete Surface Technologies sees it this way, "Our customers expect the highest quality and delivery from our polish and texture repair service. The low carbon P-20 modified steels, such as PX5, are a tremendous aid in fulfilling our commitment to getting our customers back in business as quickly as possible. In most cases we can avoid the need to pre- and post-heat the tool, as well as avoid the need for diamond lapping to get the original finish. The ability of our technicians to perform on-site repairs without pre-heating saves time and money, which are both are very valuable commodities when the mold is out of production."

 

Time to Rethink Steel Selection

Our tool building industry is comfortable using P-20. We cut our teeth on it. It's been around since the 1950s, but these are uncomfortable times. Our domestic industry is competing in a world market, but we are competing against tool builders who are using steels designed to reduce labor costs in both tool building and maintenance. Using these steels to bring manufacturing costs and leadtimes to a more competitive level will do much to allow the domestic industry to concentrate more on selling its built-in advantages-such as language, creative design, local service and quality. The playing field will begin to tilt back our way.

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