I agree with all respect to Jean he's a computer guy and not a Mech Engineer. If Tesla has cheap land and can store locally why not - remember that Japan doesn't have as much land space as the USA has

JIT just pushes the costs on to smaller suppliers who a large company can effectively bully in the same way big supermarkets bully framers.

"JIT just pushes the costs on to smaller suppliers who a large company can effectively bully in the same way big supermarkets bully framers."

This is not how the TPS works (At least not in theory. In practice, bullying may or may not happen - I don't know about any). The idea behind JIT is that you can react to changes in external circumstances faster.

Also, the suppliers should also not have huge stockpiles of parts. Then they can, too, react fast to changes in demand. But this can also cause problems: http://sloanreview.mit.edu/article/the-toyota-group-and-the-...

If you have a stamping plant, you usually have far fewer presses than part numbers. You stamp out some part, then change dies to stamp out another part. Die changing and adjustment is time-consuming and is non-productive downtime. Once a press and die set is running well, it will produce parts at a good rate without much attention, but die changing is labor-intensive. The less often you change, the lower the cost per unit.

The optimal batch size at the stamping plant may be quite different from the batch size the assembly plant wants. That means in-process inventory, stored somewhere.

In the scale of auto body parts, dies weigh many tons and cranes are needed to do a die change. Clamping a die into position is complicated. There are quick-change systems. They're expensive.[1][2]

What's probably choking Tesla is that they planned their stamping batch sizes for a much higher production rate than they can currently achieve. Much of the planning for the Model 3 production line was based on the assumption that not much would go wrong. They made hard tooling for parts before using prototype soft tooling to save time.[3] That's a win only if you get it right the first time.

(I once worked in an R&D facility for heavy hydraulic equipment. They had to deal with problems like this. People talked about "setup" a lot. A basic fact of manufacturing is that setup and changes are much more difficult than production. Once you get a production machine set up, it's mostly putting in blanks and taking out product, and that's often automatic. Setup requires skilled people. There's been a lot of talk about "agile production" and a "lot size of one", but the real economies still appear only when you make large numbers of something. Look at the pricing for some on-line service that makes custom things for you. There will be a big price break as the quantity goes up.)

[1] http://www.thefabricator.com/article/stamping/10-common-quic... [2] http://www.thefabricator.com/article/stamping/how-quick-die-... [3] https://insideevs.com/tesla-insider-speaks-out-on-problems-o...

There are two ways of doing production: large batches, like you describe, and TPS. It is counterintuitive but TPS makes small batch production more efficient and more cost effective than large batches because it looks at the production system as a whole. You may want to read up on it - Check out The Machine That Changed the World.

that's not how I recall JIT is the parts arrive just as needed on a mature production line continually making tweaks to parts is more akin to small batch production

Paywall link.

But don't Japanese companies replicate this setup even when they set up factories the USA?

They do, and it has been proven successful. I think it is unlikely that Tesla will be able to deliver high-quality cars while maintaining high efficiency if they continue like this.

The article lists another reason for not storing parts locally. It allows for rapid adjustment requests to the part supplier when Tesla realizes a part needs a slight adjustment to its design.

Very similar concept to agile software development — setup everything for rapid iteration.

Work in process is extremely expensive and large batches are more expensive than just in time production. This is the core of TPS and its not disputed.