How to accurately calculate machining time? A guide to efficient production in manufacturing

How to accurately calculate machining time? Core guide to efficient production in manufacturing

As a manufacturing practitioner, are you often troubled by these questions: the estimated processing time is seriously disconnected from the actual production? Order delay due to error in machining cycle calculation? Want to optimize your processing time for a single piece but can't find a key breakthrough? Machining time calculation may seem simple, but in fact, it is the core link that runs through production planning, cost control, and efficiency improvement, especially in the current situation where CNC machining is the mainstream, accurate calculation is an important embodiment of enterprise competitiveness. This article will dismantle the core logic of machining time calculation for you in an all-round way, from basic concepts to practical methods, from influencing factors to tool applications, and help you truly achieve efficient production.

1. Machining time calculation: You must clarify the core concepts

Before starting the calculation, it is important to clarify a few confusing core terms, which is the basis for avoiding errors in subsequent calculations.

1. Essential definition of machining time

Machining time (also known as manufacturing time) refers to the total time consumed from the start of processing to the completion of machining, including the cutting time directly involved in the processing and auxiliary auxiliary time, excluding non-machining time such as production preparation and equipment maintenance. It should be noted that the machining time in different scenarios has a specific direction: the machining time for a single workpiece is for the complete machining cycle of a single workpiece, the machining cycle may include the coherent operation time of multiple processes, and the CNC machining time emphasizes the collaborative calculation of program running time and auxiliary actions due to the high degree of automation.

2. Uniqueness of CNC machining time

CNC machining time calculations are more precise and complex compared to traditional machining. Traditional processing relies on manual operation, and the processing time is greatly affected by the operator's skills. CNC machining is controlled by programs, and the machining path and cutting parameters can be preset, so its machining time is composed of "program running time + a small amount of manual intervention time". For example, in CNC milling of a precision part, the program runtime accounts for more than 85%, and the auxiliary time is mainly focused on clamping and inspection, which is also the key reason why CNC machining time is easier to accurately estimate.

2. Processing time calculation formula: a complete disassembly from theory to practice

The core of accurate calculation of machining time is to master key formulas and flexibly adjust them based on actual working conditions. The following are the most commonly used calculation formulas and application cases to help you get started quickly.

1. Core Formula: Precise calculation of cutting time

Cutting time is a core component of machining time, which refers to the time it takes for the tool to contact the workpiece and remove material, with the formula as follows:

Cutting time (Tc)=machining allowance ÷ (feed rate x cutting width x cutting depth x material removal rate correction factor)

Simplified practical formula:

Tc =（L × n）÷（v × fz × z）

• Where: L = total machining length (mm), n = workpiece speed (r/min), v = cutting speed (m/min), fz = feed per tooth (mm / tooth), z = number of tool teeth
• Key correlation formula: Spindle speed calculation n = (1000 × v)÷(π × D) (D is the diameter of the tool or the diameter of the workpiece, mm)

Practical case: Machining 45 steel shaft parts with a diameter of 50mm, turning length of 100mm, cutting speed v=120m/min, feed per tooth fz=0.2mm / tooth, and number of tool teeth z=2.

1. Calculate the spindle speed first: n = (1000×120) ÷ (3.14×50) ≈764r/min
2. Calculate the cutting time: Tc=(100×764)÷(120×0.2×2)≈160 minutes

2. Assistance time and empty travel time cannot be ignored

Auxiliary time refers to the non-cutting time consumed to ensure the smooth progress of the cutting process, including clamping the workpiece, changing tools, measuring dimensions, lubrication and cooling, etc., usually accounting for 15%-30% of the machining time. For series production, the assistance time can be significantly reduced by standardizing operations such as the use of quick clamping fixtures.

Empty travel time is the movement time of the tool in a non-machining state (e.g., tool rapid positioning, tool retraction), and path optimization can be simulated by CAM software in CNC machining. For example, the empty travel time for a part machining was originally 20% of the total machining time, but by optimizing the tool path, it was reduced to 12%, and the overall machining efficiency was significantly improved.

3. The key role of material removal rate

Material Removal Rate (MRR) is a core metric that measures machining efficiency and directly affects cutting time using the formula:

MRR=cutting speed x cutting width x cutting depth x feed rate

MRR reference values for different materials (to be adjusted according to actual tools and equipment):

3. Key factors and optimization strategies affecting processing time

Once you have mastered the calculation method, it is more important to reduce the actual machining time through optimization. The following are the core factors affecting processing time and the optimization schemes that can be implemented.

1. Dismantling of core influencing factors

• Cutting parameters: cutting speed, feed rate, and cutting depth directly determine the cutting time, and unreasonable parameter settings will lead to inefficiency or tool damage.
• Tool Selection: Sharp, specialized tools increase cutting speed, while tool wear increases machining resistance and prolongs time. For example, carbide tools can cut 3-5 times faster than HSS tools.
• Clamping method: Traditional clamping needs to be calibrated repeatedly, which takes a long time; The use of hydraulic clamps and pneumatic clamps can shorten the clamping time by more than 50%.
• CNC program: program redundancy and unreasonable path will increase the empty travel time, for example, frequent tool lifting and retreat will waste a lot of time.
• Workpiece material: Materials with high hardness and toughness (such as stainless steel and titanium alloys) are difficult to process and take longer.

2. Practical strategies to shorten machining time

• Optimize cutting parameters: Increase cutting speed and feed within tool tolerance based on material and tool characteristics. For example, when machining aluminum alloys, the cutting speed can be increased from 150m/min to 250m/min and the cutting time can be reduced by 40%.
• Choose high-efficiency tools: Choose special tools for different materials, such as coating tools for stainless steel and diamond tools for aluminum alloys. At the same time, regularly check the wear of the tool and replace it in time.
• Simplified clamping process: Modular fixtures and quick positioning tooling are used to achieve "one-time clamping, multi-process processing". A machine shop has reduced the clamping time from an average of 8 minutes per piece to 2 minutes per piece by introducing a zero-point positioning system.
• Optimize CNC programs: use CAM software for path simulation, remove redundant instructions, and reduce empty travel; Use "forward milling" instead of "reverse milling" to reduce cutting resistance.
• Introducing High-Speed Machining Technology: High-speed machining technology can increase cutting speeds by 2-10 times, especially suitable for precision parts machining. For example, an auto parts factory has reduced the machining time of engine blocks from 45 minutes to 18 minutes after using high-speed milling technology.

3. Machining time calculation: efficient tools and software recommendations

Manual calculation efficiency is low, error is large, and accurate and fast estimation can be achieved with the help of professional tools, the following are common tools and application scenarios in the industry.

1. CAM software machining simulation

Mainstream CAM software (e.g., Mastercam, UG NX, SolidWorks CAM) has machining simulation and time estimation capabilities. By importing 3D models, setting cutting parameters, and tool paths, the software automatically calculates machining time, typically within ±5% of error rates. For example, using UG NX to simulate the five-axis machining of a complex part not only estimates machining time, but also detects path collisions to avoid errors in actual production.

2. Professional machining time estimation software

• JobShop Mate: Suitable for small to medium-volume production, it can automatically generate machining time and cost estimates based on the workpiece type, material, and process.
• Costimator: Integrates a massive cutting parameter database, supports custom process templates, and has high accuracy, widely used in aerospace, automobile manufacturing, and other industries.
• Machining Doctor: Specializes in CNC machining time calculations, supports a variety of machine tool types, and is easy to operate, suitable for frontline personnel in the workshop.

3. ERP/MES production scheduling system

ERP (Enterprise Resource Planning) and MES (Manufacturing Execution System) combine machining time with production planning and order management. For example, MES systems can collect equipment operation data in real time and dynamically adjust processing schedules to avoid overall production stagnation due to delays in a certain process. At the same time, the system can accumulate historical processing data to provide a more accurate reference for subsequent time estimation.

4. Application of cutting parameter database

Establishing an enterprise-level cutting parameter database and integrating the optimal parameter combination of different materials, tools, and equipment can greatly improve the accuracy of machining time estimation. For example, a heavy industry enterprise has established a standardized parameter library by collating the processing data of 1000+ types of workpieces, and the machining time estimation error of new workpieces has been reduced from the original 20% to less than 8%.

4. Processing time and cost quotation: directly related economic logic

Processing time is the core basis for cost accounting and quotation, and accurate time calculation can help enterprises achieve reasonable pricing and increase profit margins.

1. Machining quotation calculation logic

The core formula of the processing quotation:

Quotation=(processing time x labor rate)+material cost+tool wear+management expenses+profit

• Labor Rate: Based on equipment depreciation, labor costs, site expenses, etc., the labor hour rate for CNC machining centers is about 80-150 yuan/hour.
• Key impact: Every 10% reduction in machining time directly increases profits by 3%-5% (assuming other costs are fixed).

2. The difference between the cost of a unit and mass production

Mass production significantly reduces unit machining time and costs, as auxiliary time (e.g. programming, clamping) is allocated to more workpieces. For example:

• Single piece production: 100 minutes processing time, 30 minutes auxiliary time, total time 130 minutes / piece.
• Mass production (100 pieces): processing time 100 minutes / piece, auxiliary time 30 minutes (one-time input), total unit time 100.3 minutes / piece, cost reduction of about 23%.

5. Yigu Technology's view

The calculation of machining time is by no means a simple formula application, but a system engineering that integrates process understanding, parameter optimization, and tool application. Under the trend of intelligent manufacturing, accurate processing time estimation can not only improve production efficiency and reduce costs, but also help enterprises take the initiative in order competition. Enterprises should pay attention to the accumulation of historical data and establish standardized calculation processes with the help of digital tools such as CAM software and MES systems. At the same time, combined with new technologies such as high-speed processing and intelligent fixtures, the processing process is continuously optimized. In the future, with the in-depth application of AI technology in the manufacturing industry, processing time calculation will become more intelligent and accurate, becoming the core support for enterprises to achieve flexible production and lean manufacturing.

6. FAQ

1. Q: What is the typical range of estimated error in CNC machining time?

A: After using CAM software simulation + actual parameter calibration, the error can be controlled at ±5%-10%; If empirical estimation is relied upon alone, the error can exceed 20%.

2. Q: The proportion of auxiliary time to processing time is too high, how to optimize it?

A: Priority is given to quick clamping tools (such as zero-point positioning fixtures), standardized testing processes (such as using online measuring equipment), and "multi-station machining" mode for mass production.

3. Q: How much does the processing time vary between different materials?

A: Taking shaft parts of the same size as an example, the machining time of aluminum alloy is about 1/3-1/2 of stainless steel, and the machining time of titanium alloy is about 2-3 times that of stainless steel.

4. Q: How to manually estimate machining time without professional software?

A: You can refer to the historical machining data of similar workpieces, and estimate according to "cutting time (formula calculation) + auxiliary time (empirical value, such as 15%-30% cutting time)", it is recommended to reserve 20% buffer time for the first production.

5. Q: How can tool damage be avoided when optimizing cutting parameters?

A: Follow the principle of "step by step", with no more than 10% adjustment each time, while monitoring tool temperature and cutting force (some high-end machine tools can collect data in real time), referring to the parameter range provided by the tool manufacturer.