The tapping process of automotive parts in Akkordeon #1 needs to be comprehensively optimized from aspects such as tool selection, parameter setting, cooling and lubrication, process control and quality inspection. The following are the key techniques and implementation points:
First, tool selection and pretreatment
Tool material matching
Select tool coatings for different materials:
High-strength steel (such as 42CrMo) requires TiAlN-coated taps to enhance wear resistance and heat resistance (up to 800℃).
Aluminum alloy is recommended to use uncoated high-speed steel taps to prevent aluminum shavings from adhering. Combined with a helical groove design (groove Angle 30°-45°), the chip removal efficiency can be improved.
The thread tolerance grade should match the workpiece: for instance, when a 6H grade tap is selected for an M8×1.25 thread, the hole diameter should be controlled within Φ7.737-7.775mm.
Tool pre-adjustment and inspection
Before tapping, the tap runout needs to be calibrated. The end face runout should be ≤0.01mm and the axial runout ≤0.02mm.
Check the integrity of the tap’s cutting edge. The width of the cutting edge band should be uniform (for example, the width of the M10 tap’s cutting edge band is 0.15-0.2mm) to avoid local wear causing random threading.
Second, cooling lubrication and chip removal control
Selection of cooling method
Micro Lubrication (MQL) : Suitable for aluminum alloy tapping, with an oil mist flow rate of 50-100 mL /h, reducing adhered chips.
Internal cooling tapping: For stainless steel/titanium alloy, oil mist internal cooling (pressure 0.5-0.8MPa) is adopted. The coolant is sprayed out from the center hole of the tap and directly hits the cutting area.
Intermittent cooling: When tapping to 2/3 of the depth, pause the cooling for 0.5 seconds to utilize the thermal expansion and contraction effect to reduce the cutting force.
Chip removal path optimization
The helix Angle of the helical groove tap needs to match the material:
For brittle materials such as cast iron, use a small helix Angle (15°-25°) to prevent chip blockage.
Large helix angles (35°-45°) are used for steel parts to enhance chip removal capacity.
When tapping blind holes, reserve a 0.5-1mm tool withdrawal groove at the bottom of the hole to prevent chip accumulation.
Third, quality inspection and problem handling
Thread detection method
Pass and stop gauge inspection: If the pass gauge is fully passed and the stop gauge does not exceed two turns, it is considered qualified.
Three-needle measurement: Measure the M value to verify the median diameter, with an allowable error of ±0.04mm.
Microhardness testing: The surface hardness of the thread should be 10%-15% higher than that of the base material to ensure wear resistance.
Common Problem Handling
Thread misalignment
Reasons: The main shaft is not synchronized with the Z-axis, and the tap is worn.
Measures: Calibrate the synchronization accuracy of the machine tool and replace the worn taps.
Tap breakage
Reasons: Excessive cutting force and insufficient cooling.
Measure: Reduce the rotational speed to 80% of the calculated value and switch to internal cooling taps instead.
Poor surface roughness
Reason: Rough bottom hole, insufficient coolant.
Measures: Pre-process the bottom hole to Ra1.6μm and increase the coolant flow rate to 15L/min.
Fourth, verification of typical cases
Tapping of the M14 thread of a certain automotive engine block:
The original process adopted ordinary taps with a rotational speed of 200r/min, and the thread qualification rate was only 75%. After optimization:
Switch to TiALN-coated helical groove taps;
The rotational speed is reduced to 160r/min, and the feed rate is 280mm/min.
Cooperate with the internal cooling oil mist (pressure 0.6MPa).
Result: The qualified rate of threads has increased to 98%, and the processing time per piece has been shortened by 12%.
Thread tapping of blind hole M10 in a certain transmission housing:
The original process hole depth is 18mm, and the tap is prone to breakage. After optimization:
Tap in two sections (the first section is 12mm deep and the second section is full depth);
Add intermittent cooling (tapping for 1 second → pause for 0.3 seconds → continue).
Result: The service life of taps increased from 15 pieces to 50 pieces, and the scrap rate decreased from 8% to 1.5%.
Through the systematic application of the above process techniques, the efficiency, accuracy and tool life of tapping for automotive parts can be significantly improved, while the quality risks can be reduced. In actual production, dynamic adjustments need to be made based on the material properties, equipment capacity and processing batch.
