Tool geometry plays a key role in controlling chip form to dissipate heat. The wider and thinner chips enlarge the contact area between the chip being formed and the cutting edge, thereby reducing the accumulation of heat at the cutting edge. If the chips are thinner and generate less heat, the cutting speed can be faster. For example, when roughing with a C-type (80°) diamond blade with a standard lead angle of -5°, the chip thickness is approximately equal to the feed rate; a square blade with a mounting lead angle of 45° can be used. The cut metal (and cutting heat) spreads along the longer cutting edge. The circular blade theoretically maximizes this concept (but only when the depth of cut is small). According to Gyllengahm, very thin chips are usually obtained with a round insert when the depth of cut is small. However, considering that a circular blade having an inscribed circle of 12.7 mm has a reduced effective lead angle when the depth of cut is greater than 2 mm, it is preferable to use a square blade because the square blade still has a 45° guide at the same depth of cut. Cheng angle.
Bill Skoretz is the manager of the processing division of Patriot Forge, which supplies everything from low-alloy steels and stainless steels to special grades of aluminum alloys and titanium alloys, and sometimes to titanium alloy parts for the company's customers. When discussing the challenges of turning titanium alloys, he focused on the experience of coolant jets for turning mills. This corrosion-resistant titanium alloy grade is abrasive. Due to the resilience of titanium alloys, a positive tool geometry must be used and the shape of the tool head must be emphasized. If the bottom or front corner of the tool is too small, the tool will start to generate tension, which causes a lot of problems. Therefore, an optimum balance must be found between the positive geometrical angle of the tool head and the support of the cutting edge.
Skoretz describes the development of cutting tools from a historical perspective. Before the development of cemented carbide tools, high-speed steel tools were mainly used to cut steel. The advent of carbide tools makes it possible to use a positive geometric angle, but the machine must have sufficient power. Negative rake angle inserts only allow the titanium alloy material to fold or squash, making it difficult to remove it. But he also warned that if the positive rake angle of the blade is too large, it will also form a tensile force on the titanium alloy material. Therefore, a balance must be found between compressive and tensile stresses. He mentioned that in the past, a blade with a T-belt of 0.1 mm or 0.13 mm was used on the cutting edge. "Mainly for the safety of the blade, it is not possible to use a sharp cutting edge because it can't last long." Oil-based cutting fluids are also used in the process, but mainly rely on their lubricating properties rather than cooling capacity.
Other processing plants also have different titanium turning methods, as there are different solutions for the removal of any material.
Rayco Machine's 30% of its business is processing racing parts, many of which are expensive titanium parts, because top racing teams are willing to pay extra for lightweight, high-strength parts to keep their cars in the rules. The minimum weight while still maintaining control over the distribution of the entire body weight. For example, reducing the mass of the rotating and non-suspended parts (such as the wheel and brake components) can effectively improve acceleration and handling performance. Rayco's turning titanium parts include parts that run between the brake caliper and the rotor.
Like Skoretz, Rayco's president, Greg Cox, said that in order to successfully turn titanium alloys, a balanced approach is needed. He believes that when selecting cutting parameters, it is very important that the workpiece material cannot be pushed during processing, otherwise work hardening is likely to occur, which causes great trouble for processing. The processing parameters commonly used by Rayco are: cutting speed 120sfm, feed rate 0.13-0.20mm.
The depth of cut is also important. Again, moderate depth of cut is the best choice. Rayco's maximum depth of cut is 0.8-1mm. Rayco's titanium parts can be processed in batches of up to 200 pieces, but most are between 5-20 pieces. Cox said that Rayco is also continuing to improve the process, but care must be taken when it comes to cutting parameters, because titanium alloys are quite expensive and can't be dried out to avoid scrapping parts. The price of titanium alloys rose very quickly, rising from $47/lb to $68/lb last year. The high price of titanium alloys also tightens the inventory of workpiece materials.
Scott Holland, general manager of the R&D and manufacturing division of diving equipment manufacturer Atomic Aquatics, said that when we use titanium alloys to process underwater respirators, “we always try to continuously improve machining efficiency to reduce machining time, process more workpieces and extend Tool life.†But when they tried to machine more parts, the tool suddenly broke. Therefore, Holland hopes to achieve an optimal balance point, but this balance is not just numbers and procedures. Holland has nearly a decade of experience in titanium machining, and he relies on observing the shape of the workpiece and the tool and listening to cutting noise to master this balance. According to Holland, processing titanium alloys can also be relatively simple. “If you use sharp tools and change the tool at your own estimated time, you can only process titanium alloys in a limited range. You can try it your way, but not necessarily. It works. There are certain rules in the processing of titanium alloys. If you master these rules, you can be handy."
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