How Is a Twist Drill Made?-Twist Drill Manufacturing Process

The main twist drill manufacturing process includes spiral groove processing, heat treatment, sharpening three aspects. Because the heat treatment and subsequent grinding process are basically the same, the main difference is the twist drill part of the work of the forming process. At present, for the twist drill manufacturing process, there are mainly the following three methods: milling method, rolling method, grinding method.

Twist Drill Manufacturing Process

Milling method: Milling the required shape of the spiral groove with a forming cutter on the unhardened twist drill blank. The milling method has a large twist drill manufacturing processing range, mainly processing 2.5 to 70 mm twist drill.

The disadvantage of the milling method is the high cost of the tool, long twist drill manufacturing processing time, and finish the final shape before heat treatment processing. During heat treatment, there will happen geometry errors, almost all of which are reflected in the finished drill bit.

Rolling: the drill is rolled on a heated blank with four fan-shaped plates to form the shape of the drill bit.

Compared with the milling method, using plastic deformation of the drill bit manufacturer with less accuracy, in addition, due to the heat treatment, the geometry of the rolling twist drill will change, making it impossible to meet the requirements of drilling high-quality holes.

The main advantage of this method is to save the raw materials for the manufacture of a twist drill, with a good economy.

Grinding: The newest type of twist drill manufacturing processing.

When the wheel speed reaches 100m/s, makes the spiral groove of the twist drill to be ground out of the whole material, high-speed grinding can reduce the cutting force, greatly improve the surface quality and reduce the shape error. Compared with the milling method, the grinding method can greatly reduce the working time of a single piece, high quality, and stability.

At present, the grinding twist drill manufacturing method can only manufacture the diameter of 15 or smaller twist drills.

Technical analysis and economic effects of the three twist drill manufacturing processes.

1. Technical indicators

2. Processing efficiency

Because of the twist drill manufacturing in addition to the processing of the spiral groove, other processing processes are basically the same, for this reason, only the processing time of the spiral groove for this comparison. One hour processing 12mm straight handle twist drill several examples.

3. Performance 

The grinding twist drill has uniform hardness due to its high dimensional accuracy. Bending deformation is small, and twist drill in the process of processing has been subjected to compressive stress, and milling processing methods, twist drill is subjected to tensile stress, rolling method processing method, due to the higher temperature is difficult to control, high-speed steel materials are prone to decarburization, cracking and other phenomena, these are affected by the twist drill life.

With the same performance testing of 12mm under different process,  based on the flank wear value of VB-0.15mm

Experimental conditions:

(1) Processing materials: 45# steel tempering treatment, HB–190–200

(2) Drilling parameters; V=30m/rain,f-0.28mm/r, hole depth: 36mm, blind hole.

(3) Cutting fluid: emulsified oil and water solution

4. Economic effects

Milling: This machining method has low productivity. It is only suitable for small batch production of a single piece, with complex structure cutter, high price, and many processes, multi-specification drills need multi-specification cutter, so the manufacturing cost is high. Compared with the grinding method, this method is easy to add chips.

Rolling: 

(1) Save raw materials: As rolling is chipless processing, it can save more than 30% of high-speed steel, material utilization rate can reach more than 90%, while the material utilization rate of metal cutting process method is only 60% -70%.

(2) Increased production efficiency: The use of rolling processes can increase production efficiency by 15-20 times, and it is estimated that a four-spoke mill is equivalent to 15-20 automatic milling machines.

(3) Improving intrinsic quality: With metal cutting, a complete bar is machined by removing the material, which completely destroys the fibrous tissue of the metal, while with rolling, the fibrous layer of the metal is not cut. Moreover, it is deformed at high temperatures, which act to refine the brain tissue and improve the uniform distribution of carbides, thus improving their intrinsic quality.

(4) Cost reduction: As it can save at least more than 30% of HSS and increase labor productivity by 15-20 times, it can greatly reduce production equipment and operators; it can reduce the area of the working plant, as well as workers, measuring tools and materials.

(5) The accuracy is not high, because the heat treatment is carried out after rolling, and the geometric parameters will change accordingly.

Grinding

Higher productivity than milling method; eliminates bending deformation and saves the straightening process; high processing accuracy and stable quality. Very low scrap rate. High equipment price. Small processing range and difficult chip collection.

Therefore, the above data shows that the HSS grinding drill and rolling and milling processes are somewhat compared to the following.

1, High geometric accuracy of the grinding bit. With the rolling and milling process, the grooving of the drill must be done before quenching, which reduces the geometrical accuracy of the drill due to the distortion of the quenching process. The grinding process is to grind the groove after quenching, eliminating the deformation caused by quenching treatment, so that the geometric accuracy of the drill bit can be improved, which can make the specification of the drill bit size is finer, in order to meet the accurate processing of different sizes, improve the accuracy of the bore diameter of the parts being processed, can save the drilling and then reaming process.

2. The high finish of grinding drills. Rolled and milled drills have a finish of ▽6 or less, while milled drills have a finish of ▽8 or more. The improvement of the drill bit finish not only improves the hole diameter finish of the machined parts, eliminating the finishing process after drilling but also makes the drill bit groove chip discharge smoothly, reducing the drill bit breakage due to blockage.

2. The long service life of the grinding drill. Grinding drills have been shown to have a 1 to 2 times higher service life than rolling and milling drills. This is due to the good accuracy, high finish, sharp edges, and even stress distribution of grinding drills.

4. High productivity. The grinding process has now evolved to the stage of strong grinding, and the productivity of machining bits has reached 2 to 5 times that of milling.

In terms of accuracy/ finish/ performance/ cost, all three processes are incremental. Rolling＜Milling＜Grinding

Knowing the above process, I believe you already know how to choose the right drill bit. For more product knowledge, stay tuned for subsequent articles.