Tip Top Tap: Medical Manufacturing

Based on a geometric modification, the company reports that the contact surface between a Pionex tap has been optimized to reduce torque by up to 30%. A reduction in torque minimizes tool breakages so that the tensile strength of the tool is not exceeded.

“It does not only reduce tool breakages, but at the same time increases tool life,” Mintrone said, adding that tool life is extended about 30% to 50%. With that capability, an end user can choose to run a Pionex tap at least 25% faster than a conventional tool.

To boost productivity, end users sacrifice some tap life. Stephen Putek, product engineer I for OSG USA Inc. in St. Charles, Illinois, noted that he heard from one customer who prioritized productivity over tool life by tapping twice as fast while losing about 40% of the tap life. “But they’re happy to get these parts out the door a lot quicker. Then there are others who just need the thing to last as long as humanly possible, and they’ll do whatever it takes to make it last.”

The substrate options include HSS, powdered metal HSS and carbide, with powdered metal providing some of the benefits of both HSS and carbide, he explained. Mintrone advises against the use of a carbide tap to cut high-tensile steel because of its enhanced brittleness. A carbide tap is a better choice for threading aluminum and titanium aerospace and medical parts.

About 95% of the taps are coated, Mintrone said, mainly with TiN or TiAlN, as well as AlCrN and TiCN. The specific coating needs to provide hardness and smoothness to prevent material from sticking to the tap. “I personally advise against using an uncoated tool, mainly because of tool life reasons and chip evacuation reasons.” However, an uncoated tool is suitable when cutting a thread by hand.

Prior to coating, the taps are wet blasted with a mixture of water and sand and then dry polished with natural ingredients, as well as diamond dust, he noted. The special finishing processes impart a fine surface finish to reduce tapping friction and torque, which improves chip evacuation.

Geometry at Work

High-performance taps have geometric features to boost their capabilities. One feature is a larger core to strengthen and stabilize the tool, Mintrone noted. Another is a thread relief that’s designed to reduce contact between the flanks of the thread lands and the workpiece, preventing the chip from getting between the workpiece and the cut tap.

“It usually depends on the pitch of the tool, but we’re talking about like 0.02 mm. It sounds like it’s not much, but it is,” he said. “We can’t go too large with the relief because we want to make sure the tool keeps its self-guidance ability.”

The helix also plays a significant role, and the angle depends on the application. “When it’s a long chipping material, we usually go with a 25° up to a 45° helix to ensure good chip evacuation,” Mintrone said. “When it’s short chipping materials like cast iron or bronze, we usually go with a straight-fluted tool or maybe up to a 15° helix.”

For OSG’s A-Tap cut taps, the helix is 45° at the chamfer and transitions to 15° toward the shank. Putek described the A-Tap as the toolmaker’s go-to cut tap and “our best option on the market” for threading steel, stainless steel, cast iron and aluminum, As the helix transitions to 15°, the flute space widens to enhance chip evacuation compared to a constant 45° helix where there is more physical distance to disengage chips from the top.

“The 45° helix at the chamfer helps you increase the rake angle up front towards the chamfer, and that’s going to make it very easy for the chip to start working its way up the flute,” he said. “Then as we get farther and farther back, we want to get those chips away from the flute, and the flute space on our A-Tap actually widens towards the back.”

When it comes to the size of the chips, Jun Ahiko, product engineer II for OSG, explained that a tap with a low rake angle generates large chips while a sharp rake produces smaller chip shapes. “A-Tap has a sharp rake angle on the cutting edge. Generally speaking, a sharp cutting edge is weak and doesn’t have enough wear resistance, but the A-Tap has a V coating and a powder metal substrate in order to keep the wear resistance. A-Tap has a good balance between wear resistance and the sharp cutting edge.”

Putek added that the V coating is based off of a multilayer TiCN coating to enhance the wear resistance and extend tool life.

Regarding the substrate, Ahiko noted that the powdered metal, sintered with cobalt and vanadium, balances wear resistance and toughness. “That’s also heat treated to a hardness of approximately 65 Rockwell just to make sure that it is going to give you the maximum wear resistance.”

Carbide is still used as a substrate, Putek said, but the lower toughness and the higher price make it more suitable for niche applications, such as when tapping cast iron to resist wear because the workpiece can be quite abrasive due to its high carbon content.