What Is a Countersink?

The mounting hole is a hole designed for mounting the part on the part. Most parts of the machine need to be designed with mounting holes. The size of the mounting hole should generally be larger than the size of the largest component of the device and should be a multiple of 0.5. The surface roughness of the hole shall be marked on the design drawing. Surface roughness refers to the dimensional characteristics of the micro-geometry of the smaller pitches and minute peaks and valleys of the machined surface.

The mounting hole is a hole designed for mounting the part on the part. Most parts of the machine need to be designed with mounting holes. The size of the mounting hole should generally be larger than the size of the largest component of the device and should be a multiple of 0.5. The surface roughness of the hole shall be marked on the design drawing.

in

Surface roughness is the degree of unevenness of the surface to be processed. Due to the friction between the cutting tool and the workpiece surface during the machining process, the plastic deformation of the surface layer material when the chips are separated, the cutting speed and feed rate, and the high-frequency vibration of the process system, the peaks, valleys and gaps are formed on the surface of the workpiece The difference in meso-geometric shape, that is, the formation of mutually different surface roughness. Controlling the surface roughness of parts plays an important role in the reliability and stability of parts' mutual cooperation, reducing friction and wear, increasing contact stiffness and fatigue strength, reducing vibration and noise, and extending the service life of parts. There are more than 30 types of surface roughness evaluation parameters, and height, pitch and shape parameters are commonly used. The measurement of surface roughness includes comparison method, light section method, light wave interference method, acupuncture method, laser holographic interference method, spot method, and spot scanning method, etc., which are applicable to the measurement of different evaluation parameters and different roughness ranges, respectively. In recent years, with the computer, laser and image recognition technology, the measurement method has been greatly developed. ^[2]

Mounting hole reaming

In the forging process, the reaming is to reduce the wall thickness of the ring billet forged on a special equipment-a reaming machine, a flat forging machine, a crankshaft forging machine or a forging hammer, so that the inner and outer diameters are enlarged at the same time. This process is called reaming, and it is achieved by two-roller rolling, so it is also called "rolling reaming", and some are called "ring expansion." After reaming, the cross-sectional shape of the forging billet is close to the cross-sectional shape of the part, the geometric accuracy of the ring is greatly improved, and the utilization rate of the flat forging machine is improved. Due to reducing the tolerance margin and the residual block (tolerance on the diameter = ± 1), it can save 13-17% of the metal and reduce the cutting time by 15-25%. The reaming is most widely used in the modern bearing industry. In addition, the rims of locomotive wheels, ring parts on aero engines and gear blanks on trucks, tractors, etc. also use the method of reaming.

Reaming is to use a reaming drill to process holes that have been drilled, cast, forged or punched out. It is often used as a preparatory process before reaming. It can improve the accuracy of the hole and correct the centerline of the hole. The reaming accuracy can reach IT9, because reaming drills generally have 3 to 4 cutting edges, no transverse edges, shallow chip flutes, larger tool rigidity, better cutting conditions than drills, and better guidance than drills. Therefore, the cutting process is smooth and the machining accuracy is higher than that of drilling.

Sometimes it is encountered that there is a countersunk hole, the hole has a tapered surface, or the hole end has a convex plane, and other types of reamer (counter-drilling) are required to process.

In addition, reaming drills are often combined with other tools (such as drill bits) to form a combined tool. This allows different tasks to be performed in one stroke, which not only improves productivity, but also guarantees the mutual position requirements between the machining surfaces. . ^[3]

Mounting hole

The broaching method is used to machine the holes of the workpiece.

Broaching is characterized by high productivity. Because there are calibration teeth behind the tool, the load on these teeth is not large, and there is little wear. Therefore, the workpiece hole after drawing is highly accurate and the surface roughness is good. The best can reach IT6.

Non-ferrous metal workpieces are not suitable for grinding, and broaching is most suitable, but broaching cannot process through holes, and it is difficult to process large diameter holes or long holes. In addition, the cost of the tool is high, the accuracy is not high, the batch size is too small, and the use of a broach is not economical in cost, so the widespread application of broaching is limited.

Mounting hole boring

Use the boring method to enlarge the hole of the workpiece. Boring is one of the most commonly used hole processing methods. It can be used as roughing or finishing. It can process holes of various sizes on various parts. For holes with large diameters, boring is the only processing method. .

There are three boring methods:

(1) The workpiece rotates, the tool does not rotate and performs the feed motion-boring on a lathe machine.

(2) The workpiece is fixed, the tool rotates and feedsboring on a boring machine.

(3) The tool rotates, and the workpiece does not rotate and feeds. This is the method of boring of special equipment in mass production.

In order to improve the accuracy of boring, you can also use a floating boring block, that is, the boring block is loosely mounted on the tool bar, and the tool can be adjusted automatically. The hole is enlarged due to inaccurate installation on the tool bar or deflection of the tool center.

Boring is a machining method that uses a boring bar and a boring tool to enlarge the existing hole in the workpiece on a boring machine, lathe or other machine tools. During boring, the workpiece is fixed on the workbench, and the boring cutter is mounted on the boring bar for rotary movement, and at the same time, the worktable or boring bar is axially moved for cutting.