Preparation before CNC Prototype Manufacturing: A Comprehensive Guide

Introduction

In modern manufacturing, CNC (Computer Numerical Control) processing has become the core technology for the production of precision components. Whether it is in the automotive, aerospace, medical device industries, or mold manufacturing and electronics industries, CNC processing is widely used due to its high precision, high efficiency, and automation.

However, to achieve ideal quality and efficiency in CNC processing, the preparatory work before the processing is of vital importance. Many enterprises encounter problems such as unmet part precision, low processing efficiency, frequent tool damage, and high rework rates during production. These issues are often not caused by the machine tools themselves, but rather result from insufficient pre-production preparations.

This article will systematically outline the preparation process before CNC processing from aspects such as drawing and process planning, material confirmation of the workpiece, debugging of the machine tools, selection of cutting tools and fixtures, trial cutting and optimization. It aims to help engineers, programmers and operators better understand and master these key points.

In-depth Analysis of Engineering Drawings (2D Drawings): The Source of Everything

The first step is to create a CAD file. A CAD file (computer-aided design) can be in 2D format and can be achieved using CAD software. The CAD software will allow you to render each part of the product with the most accurate technical specifications. When carrying out this task, you must keep in mind that your workpiece plays a significant role in the feasibility of the design. This will be further explained in the context of the materials required for CNC production processing.

Comprehensive Dimension and Tolerance Analysis:

Dimension chain analysis: Understand the relationships between various dimensions, identify the design reference and process reference. Consider how to ensure that the cumulative tolerance does not exceed the limit through the processing sequence.

Tolerance Interpretation: Clearly distinguish between free tolerance (such as unmarked tolerances) and precision tolerance. A hole with a ±0.01mm tolerance and a groove with a ±0.05mm tolerance will determine which cutting tools and cutting strategies you should choose.

Geometric tolerance: This is the key point. A thorough understanding of the meanings and detection methods of symbols such as flatness, perpendicularity, concentricity, and position accuracy is essential. For instance, a hole system with a position accuracy requirement of φ0.03mm requires extremely high machine tool precision and precise alignment.

Surface roughness (Ra, Rz): The requirements of Ra 0.8μm and Ra 3.2μm determine whether you need precision milling or rough milling. This directly relates to the selection of tools, rotational speed and feed parameters, as well as the generation of the processing path.

Technical requirements: Do not overlook the annotations in the corners of the drawings. They may indicate heat treatment requirements (such as quenching to HRC50), deburring standards, special cleanliness requirements or coating indications. These subsequent processes will affect the scheduling of the processing stages.

Analysis of 3D digital model (CAD Model): Creating physical objects in the virtual world

The 3D model serves as the direct basis for programming, and its quality is of utmost importance.

Model integrity check: Open the model using CAM software, rotate and scale it, and check for any broken surfaces, gaps, overlapping surfaces or non-manifold edges. An imperfect model can lead to incorrect tool path calculations and generate abnormal G-code.

Model and drawing consistency verification: Compare the 3D model with the 2D drawings to ensure that all features, dimensions and positions are completely corresponding. Any inconsistencies found must be immediately reported, as this is the critical checkpoint to prevent batch errors.

Programming and verification of CNC programs (CAM & G-code): The language that gives life to the machining process

This is the process of writing the language that converts design ideas into the actions of the machine tool.

CAM Programming and Tool Path Planning:

Process planning: In the software, the steps of rough machining, semi-finish machining, finish machining, and deburring are all planned. Rough machining aims for material removal rate, while finish machining ensures surface quality and dimensions.

Tool selection: Choose the appropriate tool type (flat-bottomed tool, ball-head tool, round-nosed tool), material (hard alloy, high-speed steel, ceramic), and coating (TiN, TiAlN) based on the size of the feature and the hardness of the material.

Cutting parameter calculation: Based on the recommended values from the tool manufacturer, the material cutting database, and previous experience, set a scientific spindle speed (S), feed rate (F), cutting depth (Ap), and step distance (Ae). Modern CAM software usually has a powerful parameter library built-in.

Comprehensive blade path simulation:

Material removal simulation: Visually observe how the cutting tool gradually removes the material, ensuring no missed areas.

Collision check: This is the safety line for life. The simulation must include collisions that may occur between the tool handle, chuck, spindle nose, workpiece, and fixture. Any suspicious rapid movement (G00) must be carefully examined.

Overcut check: Ensure that the tool path does not accidentally cut into the retained part of the workpiece.

G-code review:

Understanding the key code segments: Programmers and operators should be able to understand the basic G-code. Key points to focus on: Program header (safety initialization instructions), tool change instruction (Txx M06), tool length compensation (G43 Hxx), tool radius compensation (G41/G42 Dxx), spindle start/stop (M03/M05), coolant switch (M08/M09), and loop instructions (G81-G89).

Logic check: Verify whether the program is performing XY plane movement at a safe height (G00 Z50.) to avoid directly cutting into the workpiece.

Setting up a CNC machine involves preparing the CNC machine for the process. This setup depends on whether you are using a high-capacity or low-capacity process. This includes different machines used in the process, such as lathes, milling machines, grinders, etc. Additionally, every excellent company handling any CNC production processing must have a competent and skilled engineer responsible for the process.

Workpiece material and blank preparation

Material confirmation

Check whether the material grade is consistent with the drawing.

Confirm the heat treatment status of the materials (such as annealing, quenching, tempering, etc.).

Check whether there are cracks, rust or pores on the surface of the material.

Raw Material Selection

The different types of raw materials such as bars, plates, castings, forgings, etc., have a significant impact on the CNC processing paths and the selection of fixtures.

Try to select the blank that is as close as possible to the final part size in order to reduce the cutting allowance.

Preprocessing

The large-sized blanks need to be preprocessed to ensure the stability of clamping.

For materials with residual stress, stress-relieving treatment can be carried out to prevent subsequent deformation.

Machine tool equipment inspection and commissioning

Inspection of machine tool status

Machine tool accuracy inspection (main shaft runout, guide rail accuracy).

Are the electrical system, lubrication system and cooling system functioning properly?

Verify that the machine tool parameters are set in accordance with the process requirements.

Tooling and Fixture Calibration

Check whether the three-jaw chuck, vise and special fixtures are securely fastened.

Confirm the positioning accuracy of the fixture. If necessary, make corrections.

If it is for mass production, fast clamping and automated fixtures need to be considered.

First piece trial cutting and optimization

First piece trial cutting process

Clamping the workpiece → Setting the tool position → Running the program → Inspection.

Measure the key dimensions and inspect the surface quality.

Adjust the tool compensation and process parameters.

Data Recording and Process Optimization

Record the wear patterns of the tools and optimize the management of tool lifespan.

Optimize the processing parameters based on the trial-cut data to enhance efficiency.

For mass production, formulate standard operation instructions.

Common Problems and Solutions for Preparations Before CNC Processing

Question 1: Deformation during part processing
→ Conduct material aging treatment in advance and optimize the fixture design.

Question 2: The tool life is too short.
→ Adjust the cutting parameters and select the appropriate coated tool.

Conclusion: Transform preparation into habit, establish excellence as a standard

The preparatory work before CNC processing is far from being merely a “prepare for it”. It is a complex system that integrates engineering technology, management art, and the spirit of craftsmanship. It requires practitioners to possess rigorous logic, meticulous attitude, and rich experience.

From the in-depth analysis of the drawings to the meticulous improvement of tool management; from the daily maintenance of the machine tools to the meticulous attention to detail in the first-piece inspection, the perfect execution of every step has jointly created the outstanding quality and high efficiency of the final product.