Stainless steel also called inox steel which is a type of steel alloy with improved properties and performance. In this article, dajinprecision.com introduces the problems and solutions of CNC thread cutting tools in stainless steel machining and different stainless steel series, models, characteristics, applications and more. 

Solutions of CNC Cutting Tools Problems for Stainless Steel Thread Machining

Poor surface roughness of the stainless steel thread after CNC cutting, fish scale corrugation and blade jamming are the most frequently occurred phenomena in CNC stainless steel thread turning, the reasons including:

1. The edge clearance angle of the blade on both sides of the thread lathe tool is too small, and the friction between the two sides of the blade and the back thread surface deteriorates the machining surface.

2. When the front angle of the thread turning tool is too small, the cutting edge is not sharp enough, the chip can't be cut smoothly, but is partially squeezed or torn, which causes the thread surface to be very rough. When the front angle is too large, the blade strength is weakened and it is easy to wear, crack, and burr, which is more likely to cause vibration and cause ripple on the thread surface.

- Solution: you should choose the appropriate rake angle according to the types of stainless steel. When turning concentrated sulfuric acid with stainless steel threads, a smaller front angle should be used than for turning 2Cr13 stainless steel threads. The cutting edges on both sides of the turning tool should have a narrow edge to avoid rapid wear. When cutting 2Cr13, 1Cr17, 4Cr13, the cutting edge should be as sharp as possible, otherwise it is not easy to achieve the desired good surface roughness.

3. The thread cutter blade is blunt, and the actual front and rear angles reduced. The chips are severely squeezed during the process, which increases the cutting force and vibration during the cutting process, and the machining surface deteriorates severely. 

- Solution: when turning stainless steel thread, you must keep the sharpness of the blade at any time and replace the cutter head in time.

4. The thread turning tool is not firmly fixed, the cutter head is extended too long, the rigidity of the tool bar is not enough, or the machine tool has poor precision, the spindle is loose, and the tool holder is loose, which causes vibration and corrugation on the thread surface. 

- Solution: it is necessary to pay attention to the operation of CNC machines, tools and workpieces, to make the system rigid enough. When installing the CNC turning tool, in addition to ensuring the firm installation and no looseness, the cutting tool tip should be slightly higher than the center of the workpiece by 0.2 to 0.5 mm, it must not be lower than the center to avoid tying the knife.

5. Straight cutting method should be avoided when turning the thread. Due to the long contact length of the chips on the left and right sides, vibration is easy to occur, so that the load on the tool tip is increased, causing vibration and increasing resistance during chip removal. 

- Solution: it is better to use both sides alternate cutting for the stainless steel threads machining.

6. The matching degree of cutting amount in the CNC thread cutting process directly affects the processing efficiency. Too small amount will cause the tool to wear out more seriously, while too large amount will cause the tool to break. 

- Solution: control the feed amount.

In order to obtain the optimum tool life, the workpiece diameter should not be larger than the thread diameter 0.14 mm, and the feed should be not less than 0.05 mm each time. The total amount of CNC thread cutting should be set at about 0.1mm. The first cutting depth should be 150~200 (percent) of the tool nose radius (R), and the maximum should not exceed 0.5mm. For austenitic stainless steel, the feed should be not less than 0.08 mm each time. 

Types, Models, Characteristics, Applications and Differences of Stainless Steel

The stainless steel models are represented by numbers, including 200 series, 300 series, 400 series, 500 series and 600 series, which are the representation methods of the United States.

1. 200 series: 201, 202, etc.

Manganese instead of nickel, poor corrosion resistance, can be used as a cheap substitute for 300 Series. Strictly speaking, it is not stainless steel.

2. 300 series:

(1) 301 - good ductility and weldability, used for forming products. It can also be hardened quickly by CNC machining. Better wear resistance and fatigue strength than 304 stainless steel.

(2) 302 - corrosion resistance is the same as 304, and the strength is better due to the relatively high carbon content.

(3) 303 - it is easier to cut than 304 by adding a small amount of sulfur and phosphorus.

(4) 304 - the 18/8 stainless steel, 304 stainless steel is a general model and one of the most common model in stainless steel, with high temperature resistance of 800 degrees, good machinability and high toughness. It is widely used in industry, furniture decoration industry, food and medical industry.

(5) 309 - better temperature resistance than 304.

(6) 316 - after 304, the second most widely used stainless steel, mainly used in food industry and surgical equipment, adding molybdenum element to obtain a special corrosion-resistant structure. It is also used as "marine steel" because it has better chloride corrosion resistance than 304. SS316 is commonly used in nuclear fuel recovery units. Grade 18/10 stainless steel also generally meets this application level.

(7) 321 - except that the addition of titanium reduces the risk of material weld corrosion, other properties are similar to 304.

3. 400 series: Ferritic and martensitic stainless steel. 400 series stainless steel is an alloy of iron, carbon and chromium. This stainless steel has martensitic structure and iron element, so it has normal magnetic properties. 400 series stainless steel has a strong resistance to high temperature oxidation, compared with carbon steel, its physical and mechanical properties have been further improved. Most 400 series stainless steels can be heat treated.

(1) 408 - good heat resistance, weak corrosion resistance, 11% Cr, 8% Ni.

(2) 409H: good machinability, weldability, high temperature oxidation resistance, and the temperature range of bearing is from room temperature to 575 ℃， widely used in the automobile exhaust system.

(3) 409L: control the content of C and N in the steel, so the weldability, formability and corrosion resistance are excellent; containing 11% Cr, it is a ferritic stainless steel with BCC structure at high temperature and normal temperature; because Ti element is added, its high temperature corrosion resistance and high temperature strength are good. Air oxidation and corrosion resistance below 750 ℃. It is used in automobile exhaust pipe, heat exchanger, container and other products without heat treatment after welding.

(4) 410: typical type martensite stainless steel, with high strength and hardness (magnetic); poor corrosion resistance, not suitable for severe corrosion environment; low C content, good machinability, and surface hardening by heat treatment.

(5) 410L: on the basis of stainless steel 410, the C content is reduced, and its process possibilty, welding deformation resistance and high temperature oxidation resistance are excellent. It is used in mechanical structure parts, engine exhaust pipe, boiler combustion chamber and burner.

(6) 420J1: high hardness and good corrosion resistance after quenching. It is applied to tableware (knife), turbine blade.

(7) 420J2: typical type martensite stainless steel with high strength and hardness (magnetic); poor corrosion resistance, poor processing formability and good wear resistance; capable of heat treatment to improve mechanical properties. After quenching, the hardness is higher than that of 420J1. It is widely used in cutting tools, CNC turning parts nozzles, valves, ruler and tableware. 

(8) 430: typical type ferritic stainless steel, it has good thermal expansion rate, corrosion resistance, formability and oxidation resistance. Suitable for heat-resistant appliances, burners, household appliances, class 2 tableware, kitchen sink. Low price and good machinability are ideal substitutes for SUS304.

(9) 436L: good heat resistance and wear resistance. Because it contains niobium element, it has excellent processability and weldability. 

(10) 440 - high strength cutting tool steel, with slightly higher carbon content, can obtain higher yield strength after proper heat treatment, and the hardness can reach 58 HRC, which is one of the hardest stainless steels. The most common application example is razor blade. There are 4 common models: 440A, 440b, 440C, and 440F.

4. 500 series: heat resistant chromium alloy steel. A certain amount of nickel and nitrogen are added to the material and treated with rare earth to improve the diffusion ability of chromium atom and expand the austenite structure, thus improving the heat resistance and heat strength of the alloy steel, which is widely used in thermal power plant boiler nozzle, pre combustion chamber, door hole, etc.

5. 600 series: Martensitic precipitation hardening stainless steel. 

630 - the most commonly used precipitation hardening stainless steel mod

Dajin Precision providing CNC stainless steel turning services of a variety of stainless steel models and custom stainless steel parts conforms to ISO9001: 2015 quality standards and clients' requirements.