In the era of rapid technological advancement, spurred by the third scientific and technological revolution, industries are becoming increasingly intelligent and information-driven. For those of us in the field of mechanical design, manufacturing, and automation, the question arises: how can we leverage these developments to excel as CNC machinists?
A qualified CNC machinist must have a solid foundation of knowledge. This includes a deep understanding of mathematics, engineering drawing, physics, English, professional skills, and the innovative ability to adapt to the ever-evolving manufacturing industry. Below are 41 essential questions and answers that highlight the key knowledge areas every CNC machinist should master.
Core Knowledge for CNC Machinists
- What are the three methods of workpiece clamping?
- Clamping in the fixture.
- Alignment and clamping directly.
- Line alignment and clamping.
- What does the process system include?
- Machine tool, workpiece, fixture, tool.
- What are the components of the machining process?
- Rough machining, semi-finishing, finishing, super-finishing.
- How are benchmarks classified?
- Design reference.
- Process reference: process, measurement, assembly, positioning (original, additional): (rough reference, fine reference).
- What does machining accuracy include?
- Size accuracy.
- Shape accuracy.
- Position accuracy.
Understanding Machining Errors and Accuracy
- What are the original errors in the processing process?
- Principle error, positioning error, adjustment error, tool error, fixture error, machine tool spindle rotation error, guideway error, transmission error, forced deformation of the process system, thermal deformation, tool wear, measurement error, residual stress error.
- How does process system stiffness affect machining accuracy?
- Shape error caused by the change in the cutting force action point.
- Machining error due to cutting force variation.
- Error from clamping force and gravity.
- Influence of transmission force and inertial force.
- What are the guiding errors and spindle rotation errors in machine tools?
- Guide rail displacement error.
- Spindle radial circular run-out, axial circular run-out, and inclination swing.
- What is the phenomenon of “error double reflection”?
- When the process system error deformation causes the error of the blank to reflect on the workpiece. To reduce this, measures such as increasing tool passes, enhancing system stiffness, reducing feed rate, and improving blank precision are taken.
- How is transmission error in the machine tool transmission chain analyzed?
- Error is measured by the angle error (Δφ) of the end element. Measures to reduce this include shortening the transmission chain, minimizing transmission ratios, and using correction devices.
Enhancing Machining Processes and Productivity
- What are the ways to ensure and improve machining accuracy?
- Error prevention technology: Reducing, transferring, and averaging original errors.
- Error compensation technology: Online detection, automatic grinding, and controlling decisive error factors.
- What are the geometric components of a processed surface?
- Surface roughness, waviness, grain direction, and defects.
- What are the physical and chemical properties of the surface layer material?
- Cold work hardening, metallographic deformation, and residual stress.
- Factors affecting surface roughness during cutting?
- Determined by the height of the remaining cutting area, tool nose radius, deflection angles, and feed rate.
- Factors affecting surface roughness during grinding?
- Grinding amount, wheel particle size, and wheel dressing impact surface roughness.
Dealing with Machining Challenges
- Factors affecting cold work hardening of the cutting surface?
- Cutting amount, tool geometry, and material properties.
- What is grinding tempering burn?
- Tempering burn occurs when the temperature in the grinding zone exceeds certain thresholds, leading to a change in metal structure and hardness.
- How to prevent and treat machining vibration?
- Enhance process system stability, use vibration reduction devices, and improve dynamic characteristics.
- Application of machining technology?
- Machining process cards, process cards, and process sheets are used for different production scales.
- Principles for selecting rough and fine benchmarks?
- Rough: Ensure mutual position, machining allowance, and ease of clamping.
- Fine: Overlap, unified, mutual, and self-datum principles.
Processing Stages and Efficiency
- Principles of the process sequence?
- Process reference planes first, surfaces before holes, and main surfaces before secondary ones. Rough machining is done before finishing.
- How to divide processing stages?
- Rough, semi-finishing, finishing, and precision finishing stages. This division helps manage thermal deformation, eliminate residual stress, and optimize resource use.
- Factors affecting process margin?
- Dimensional tolerance, surface roughness, and spatial errors from previous processes.
- Components of the working hours quota?
- Total quota = Single piece time + Quasi-final time / Number of pieces.
- Technological ways to improve productivity?
- Shorten basic time, reduce overlap between auxiliary and basic times, streamline work setup, and minimize preparation time.
Assembly Process and Accuracy
- Main contents of assembly process specification?
- Analyze product drawings, divide assembly units, draft assembly sequence, calculate time quota, and determine technical requirements.
- Considerations in machine structure assembly?
- Structure should allow independent assembly units, minimize rework, and facilitate easy assembly/disassembly.
- What does assembly accuracy include?
- Mutual position, movement, and coordination accuracy.
- Key points when determining assembly size chain?
- Simplify as necessary, ensure consistency across components, and supervise accuracy in different directions.
- Methods to ensure assembly accuracy?
- Interchange, selection, repair, and adjustment methods.
Tools, Fixtures, and Clamping
- Components and functions of a machine tool fixture?
- Positioning, tool guiding, clamping elements, and connections ensure workpiece accuracy, production efficiency, and safety.
- Classification of machine tool fixtures?
- Universal, special, adjustable, combined, and group fixtures.
- Common positioning components for planar workpieces?
- Fixed, adjustable, self-positioning, and auxiliary supports.
- Positioning components for cylindrical holes?
- Mandrel and positioning pin.
- Positioning components for outer circular surfaces?
- V-shaped blocks.
- Design principles for “two pins on one side” positioning?
- Determine center distance, cylindrical pin diameter, and diamond pin specifications.
- Aspects of positioning error?
- Reference position error and reference inaccuracy coincidence error.
- Basic requirements for workpiece clamping devices?
- Maintain correct position, apply appropriate clamping force, and ensure ease of operation and safety.
- Elements determining clamping force?
- Size, direction, and action point, ensuring consistency with workpiece rigidity and cutting forces.
- Common clamping mechanisms?
- Wedge, spiral, eccentric, hinge, centering, and linkage clamping structures.
- Classification of drilling jigs by structural characteristics?
- Fixed, rotary, flip, cover, and sliding column jigs. Drill sleeves can be fixed, replaceable, quick-change, or special.
The Future of CNC Machinists
CNC machinists must possess “independent innovation” and “flexibility.” In a rapidly changing market, the more knowledge and experience a CNC machinist has, the better they can adapt to new challenges and contribute to the technological advancement of modern enterprises.
If you need expert CNC machining services, reach out to us today for a quote. Our team of engineers and machinists is ready to help you complete your projects with precision and expertise in CNC machining, sheet metal fabrication, and 3D printing. Keep learning and stay ahead with our resources and blogs.
