Analysis of Drilling and Reaming Processes

In the vast field of mechanical processing, hole machining is an extremely critical link. Statistics show that in typical mechanical parts, parts with holes account for as high as 60%-85%, and the quality of these holes directly affects the assembly accuracy and performance of products. This article will analyze two key hole machining technologies: drilling and reaming, and elaborate on the characteristics of various processes.

 

1. Drilling

 

1.1 Definition: It is a process for machining initial holes in solid materials, and the most commonly used tool is the twist drill. Through the rotational cutting and axial feeding of the drill bit, the material is cut into chips and discharged to form a basic hole structure.

1.2 Key Points

1.2.1 Accuracy Range

The dimensional accuracy is generally IT13-IT11 (tolerance ±0.1-0.3mm), and the surface is relatively rough (Ra50-12.5μm), which is suitable for non-fitting holes such as bolt holes and thread bottom holes.

 

1.2.2 Operating Skills:

(1) Choose the right drill bit: high-speed steel or coated drill bits for steel parts, and solid carbide drill bits for stainless steel.

(2) Control parameters: high rotation speed (1500-3000r/min) for soft materials (aluminum, copper), and medium rotation speed (800-1500r/min) for hard materials (steel).​

(3) Ensure good positioning: for high-precision holes, center holes must be drilled first; before drilling on inclined surfaces, mill to a flat surface or use a spherical drill bit to prevent slipping.

 

1.3 Common Drilling Problems and Solutions

1.3.1 Drilling Deviation (Drill Bit Run-out)

(1) Causes: Insufficient rigidity of the drill bit, unfixed workpiece, uneven feeding force.

(2) Solutions：

• First use a center drill for positioning.
• Reduce the feeding speed and maintain uniform pressure.
• Use guide sleeves or drilling dies.

 

1.3.2 Rough Hole Wall (Lots of Burrs)

(1) Causes: Drill bit wear, improper cutting parameters, poor chip removal.

(2) Solutions：

• Replace with a sharp drill bit.
• Reduce the feed rate and increase the rotation speed.
• Use cutting fluid to improve chip removal.

 

1.3.3 Drill Bit Breakage

(1) Causes: Excessive feeding, dull drill bit, chip blockage.

(2) Solutions:

• Check the wear of the drill bit.
• Use peck drilling (G83 cycle) for deep holes.
• Ensure sufficient cooling.

 

2. Reaming

 

2.1 Definition: It is used for finishing existing holes to improve their dimensional accuracy and surface finish. Reaming uses a reamer on the basis of a drilled or bored hole to remove a small amount of material, thereby obtaining a more accurate hole diameter and a smoother surface.

 

2.2 Key Points

2.2.1 Accuracy Range

The dimensional accuracy can reach IT9-IT6 (IT5 for precision reaming), and the surface is smooth (Ra3.2-0.2μm), which is suitable for fitting holes such as bearing holes and positioning pin holes.

 

2.2.2 Operating Skills:

(1) Control the allowance: 0.15-0.25mm for rough reaming, 0.05-0.1mm for precision reaming, and appropriately increase for hard materials.

(2) Low-speed processing: when high-speed steel reamers are used to process steel parts, the rotation speed is 3-8m/min to avoid overheating and wear.

(3) Choose the right cutting fluid: extreme pressure emulsion for steel parts, kerosene for aluminum/copper, and dry cutting for cast iron.

 

2.3 Common Reaming Problems and Solutions

2.3.1 Over-sized Hole Diameter (Out of Tolerance)

(1) Causes: Reamer wear, excessively high cutting speed, excessive allowance.

(2) Solutions：

• Replace with a new reamer.
• Reduce the cutting speed by 20%.
• Control the allowance of the pre-machined hole (0.1-0.2mm).

 

2.3.2 Rough Hole Wall (With Chatter Marks)

(1) Causes: Uneven feeding, insufficient system rigidity, insufficient cutting fluid.

(2) Solutions：

• Use a floating reamer head (to reduce vibration).
• Increase the concentration of cutting fluid (10% emulsion for steel parts).
• Reduce the feed rate (f=0.05-0.1mm/rev for precision reaming).

 

2.3.3 Reamer Edge Chipping or Seizing

(1) Causes: Excessive allowance, reverse rotation during tool withdrawal, chip blockage.

(2) Solutions：

• Control the allowance (carry out rough reaming → precision reaming step by step).
• Keep forward rotation during tool withdrawal (use G85 cycle for numerical control).
• Increase the number of chip removal during deep hole reaming.

 

3. Cooperative scenarios：High-precision holes are usually first drilled with allowances and then finished by reaming, such as engine bearing holes.

 

Conclusion:

Mastering the basic logic of these two processes can meet most hole machining needs, and efficiently complete everything from simple mounting holes to precision fitting holes.