Recently, in the cost model of mold processing, the more I found that the cost accounting of mechanical processing is simply the "hardest hit area of empiricism".

somewhatCNCCost, most procurement and cost personnel are mostly "this machine costs 80 yuan or 100 yuan per hour", either according to the market conditions, or staring at the equipment price and labor salary to calculate the rate. But the real bottleneck is never "how much time it costs", but "how long it takes to process" - the same mold part, some people count 2 hours, some people count 5 hours, saying "different workpieces and different processes are not reference", and finally the cost accounting becomes "to see who is experienced", and there is nowhere to start reducing costs.

In fact, the cost of machining should have jumped out of the "empirical theory" a long time ago. There is only one core: first understand the process thoroughly, then build standards, and calculate detailed accounts. Take CNC as an example, from the process to the tool, fromCutting parametersWhen it comes to working hour statistics, there are new algorithms that can be implemented, and today I will dismantle these dry goods for you, and you can try to use them after reading them.

Let's break it clearly: the pain points of machining costs are all in "not understanding the process"

Many people calculate the cost of machining and go around the process. For example, when calculating CNC working hours, regardless of whether the part needs to be "roughing + heat treatment + finishing", or only "roughing", directly estimating the time based on "about the same", the result is ridiculously different.

For example, for the same mold cavity, engineer A counts 3 hours and B counts 6 hours. When asked why, A said, "Use a large throwing knife for rough opening, and use a light knife."Round nose knife, very fast"; B said, "I am afraid that the size is inaccurate, so I use a small tool to mill slowly, and I need to test it several times." The two argued about this for a long time, and finally found that they did not follow the process standard - the hardness of the parts was 50HRC, and a coated carbide knife should be used, A used an ordinary high-speed steel knife (easy to chip), and B did not calculate the allowance after heat treatment (1mm more milled).

This is the problem: if you don't understand the process, no matter how powerful the experience is, it will go astray. The cost of machining is at the heart of the process, such as:

Do you want heat treatment? How much margin is left before heat treatment? (Leaving too much labor and time, leaving less is afraid of scrapping)

Use a round nose knife or a large flying knife for rough opening? (Large fly knives are highly efficient, but have R-angle limitations)

cutting speed,The amount of knife eating on the backHow to decide? (Soft materials can be milled quickly, hard materials can go slowly)

If these are not figured out, the cost can only be a "pat on the head", let alone reduce costs.

New algorithm for machining costs: from "estimating time" to "calculating detailed accounts"

Don't worry about "how much is the hourly cost", first calculate the "working hours". Taking CNC as an example, share a set of implementable working hour algorithms, step by step, from process to statistics.

1. Pre-determined process: Don't come up and count the time

Before calculating hours, answer 3 questions:

How many processes do parts take? For example, "roughing→ heat treatment→finishing", or directly "roughing + semi-finishing"? Heat treatment will make the parts harder, and the subsequent finishing will have to change the tool and adjust the parameters, and the working hours will definitely be different.

How much allowance is left for each process? For example, for aluminum alloy parts, it is enough to leave a finishing allowance of 0.2mm after rough machining; However, stainless steel is hard, so it must be left 0.5mm, otherwise the deformation will be super poor after heat treatment.

Do you want special treatment? For example, if the cavity has a deep cavity, you have to use an extended knife, and the processing speed should be slow; There are many curved surfaces, so you have to use a ball knife with a 30% lower efficiency than a round nose knife.

For example, the mold core of the die-casting mold did not consider heat treatment at the beginning, and it was calculated as 2.5 hours according to "roughing + finishing", but later it was found that it was necessary to go firstTemperingAt 45HRC, a "heat treatment and fine milling" must be added, and wear-resistant tools must be changed, and the final working time is adjusted to 4 hours - this is accurate.

2. Select the tool + set the parameters: Don't choose the tool based on feeling

If the tool is chosen correctly, the man-hours can be saved in half. The key is to "follow the tool manual, not by experience".

For example, open bold:

The large surface plane uses a "large diameter flying knife" (such as φ50mm), and the back eating capacity can reach 5mm, which is highly efficient.

The cavity with R angle uses a "round nose cutter" (such as R5mm), which can mill the R angle at one time without the need for repairs;

For soft materials (such as aluminum), use a "3-flute end mill" for fast chip removal; Hard materials (e.g. pre-hardened steel) are used with a "2-edge coated knife", which is wear-resistant.

Don't blindly adjust the parameters, just look at the recommended values in the tool manual. For example, YG-1's φ10mm round nose cutter for processing 45# steel (200HB) is recommended to "cut 0.1mm per edge, rotation speed 8000rpm, feed speed 4800mm/min" - according to this parameter, milling a 100mm long surface only takes 2.5 seconds.

3. Final calculation of working hours: "material removal rate" is used as the standard

The most crucial step: stop "estimating hours" and use "material removal rate (g/min)".

To put it simply, weigh the parts before processing, weigh them after processing, calculate the difference (that is, the weight of the material removed), and then divide by "the weight of the material removed per unit of time" to calculate the processing time.

Like what:

1000g before parts processing, 800g after processing, 200g removed;

Measured CNC machining, 20g of material can be removed per minute (including auxiliary time);

Processing time = 200g÷20g/min=10min.

This method can be used whether it is turning, milling, grinding, EDM, or wire cutting. Moreover, it can count "auxiliary time" (loading and unloading, tool setting, and measurement), which is more accurate than simply calculating "cutting time".

A mold factory used this method to build a database: the "material removal rate" of different materials (aluminum, steel, copper), different processes (roughing, finish milling), and different tools was recorded, and now the error in calculating labor hours does not exceed 10%, and the quotation is twice as fast as before.

Finally, I would like to say: there are standards first, and then there is the possibility of cost reduction

Some people say that "machining is too flexible to standardize", but you think: if you don't even know "how long it will take to finish processing", how to find room for cost reduction?

For example, if you find that a certain part has a "material removal rate of only 15g/min", which is lower than the average of 20g/min in the database, you can check the reason: Is the tool selected small? Or are the parameters not adjusted? Or is the operator too slow to use the knife? If you find a problem, you can fix it - replace the φ8mm knife with a φ10mm knife and the removal rate is 18g/min, saving 1.5 minutes of labor time per piece, and mass production of 1000 pieces can save 25 hours (equivalent to 3 working days).

The cost reduction of machining has never been "cutting suppliers' time costs", but "making the process fine and building standards". People who do costs must first understand the process and then use data to speak, don't be "cost people who only read quotations", but "cost people who can go to the workshop to talk to the master about tools and parameters".

Next time you calculate the machining cost, don't ask "how much does it cost", go to the workshop first: how many processes does this part take? What knife to use? How much material can be milled out per minute? If you understand these things, the cost will change from "based on feeling" to "calculated accurately", and the cost reduction will naturally have a direction.

Finally, I would like to thank Li Gong, Liu Gong, Tang Gong, Huang Gong, Manager Liu for selfless help to me, Ou expert, Feng Gong, Xu expert, Wang expert for selfless help off-site,

I especially appreciate the meaning of the existence of cost people in a sentence from expert Wang: make the cost visible, let the cost analysis no longer consume the cost, I also specifically asked for her opinion, who is interested in the cost can contact her 13917597929, is a professional automotive industry cost expert, whether it is the concept and sense of value is very nice.