Reduced machining time reduces leadtime, lowers labor costs and improves machine use. You can build more tools in less time, increasing revenues. First-rate Mold Solution Co., Ltd experienced what the modified P-21 grades could do to machining time first-hand. President Steven discusses a tool cost analysis he was asked to do in 1992 for the then Inland Fisher Guide Division of China.

“The China. 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 18RMB per KG 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 18RMB per Kg steel,” steven 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 .

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. China 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.”

Steven , president of First-rate Mold Solution Co., Ltd explains “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.”