Just-in-time (JIT) manufacturing has many aliases: Short-Cycle Manufacturing, Continuous-Flow Manufacturing, the Kanban System (Kanban itself being only an element of JIT manufacturing), and the Toyota Production System. That last one is in its fifties, codified and instituted at Toyota in the 1960s. The notion arrived on Western shores roughly 20 years later.
Today, manufacturers are leapfrogging the just-in-time concept and blurring lines in the digital space in which body parts, mechanical systems, and designs live before they hit the reality of metal, plastic, and glass.
At Toyota’s Texas truck plant, which builds Tacomas and Tundras, the lead engineer responsible for those products works right on the factory floor, overseeing actual production and end-of-line quality. This truck plant lives in arguably the most agile manufacturing ecosystem in the US, with the vast majority of suppliers inside the factory, building parts on an “immediately in time” basis.
Powerful digital design and manufacturing tools are setting new trends in manufacturing, and parts and tooling are redesigned during production with much greater flexibility. We sat down with Mike Sweers, chief engineer for the company’s trucks, to discuss the changes the company has made in how parts and systems are integrated in the most tangible ways.
In Toyota’s ecology, Sweers is a combination of chief engineer, vehicle line manager, product marketer, spokesman, and insurer of profitability. “It’s really a cradle-to-grave concept of production,” he told us. “From the very beginning where we need to identify an appropriate budget for a new generation of a vehicle all the way to any possible service issues in the field. I stay with that vehicle from birth.”
But like many engineers, Sweers has a mechanical background, starting “on the board,” as he put it, beginning his career at a drafting table.
Flexibility in design
A lot of what exists in computer-assisted design (CAD) goes far beyond what Sweers and his contemporaries could even conceptualize when they began their careers. The process still begins with sketches and design, where styling is decided and 1:5 scale models in clay are made. But now, manufacturers also create the mathematical data needed for tooling and stamping feasibility right at that time.
Before, designers and engineers used to make templates. Now, that mathematical and dimensional data is fed into a computer numerical control mill to create the clay model. A rough cut completed, human hands then hone the model.
Next, the design goes through digital surfacing (scanning/sampling), and that data is cleaned up within CAD. That CAD data is sent to Engineering and Design, which starts breaking it into forms and parts for both interior and exterior work. The mathematical data in CAD then goes into a computer-assisted manufacturing (CAM) process.
But with sheet metal body parts—which want to bounce back a bit from the form at which they first emerge from a stamping—they have to overbend or cheat to yield a proper final angle. This “compensation” data is poured into the machinery and stamping.
These hard pieces, like body and mechanical parts, go through test production before actual production, but some don’t. Instrument panels, grilles, and other pieces that are not crash-critical will go through FEA (Finite Element Analysis). That means digitally testing them for durability, aero, structural strength, and so on. With these components, there’s a constant cycle of design iteration to get all parameters met before any tangible part is made.
Virtual assembly effort
Design engineers and production engineers meet before anything is actually produced and essentially put the car together in a virtual space beforehand. If the parts don’t go together well in that environment, they make application changes right then.
This digital assembly can also inform the building sequence of parts and subassemblies, which may turn out very different from how they were planned. This process not only helps with the mechanical fitment of parts together but also the ergonomics of assembly on the production line.
“We digitally put them together by an assembly line worker with human ergonomics,” Sweers said. “This also uncovers any potential limitations of the vehicle’s structure in the process of assembly. It prevents roadblocks due to unforeseen interferences. But we also sometimes add variable design interferences like weatherstripping.”
Once all the math data is in place, one design or body engineer can take a sectioning plane—essentially a digital magnifying glass—over any section or subassembly of the vehicle and see where the interferences might be according to the rules established by the team. This tool also shows the thickness of the parts and the mating surfaces, all the relevant data of that part in 3D.
Sweers cited a recent example of a problem discovered and averted ahead of parts production as a result of this virtual assembly process.
“The current Tacoma Off-Road grille is styled to look like it’s stamped from metal,” said Sweers. “We found through CAD and a fluid dynamics software program that the actual shape of the grille holes created a pressure and flow drop from the specification.” The team knew that flow spec was required for the vehicle’s main and peripheral (transmission and oil) cooling systems. They literally had an airflow problem.
But rather than stop the pre-production schedule just ahead of the vehicle’s launch, the team was quickly able to modify the shape and radius of the holes in the grille until reaching the designers’ own self-imposed cubic feet per minute flow rate on the back side of that grille.
The actual change was, to a layman, miniscule. The team changed the pitch of the bottom elements in the grille by a ½ degree and lowered it slightly. “That fixed the problem and we never left the digital space,” he said.
At roughly the same time, the Tacoma team was confirming body panel configuration when it discovered the overall coefficient of drag (Cd) was slightly higher than what was agreed upon during design. Pride was at stake, as marketing wanted to claim a best-in-class Cd, but there were follow-on effects for noise and highway fuel economy.
The team found a solution by slightly reshaping the end contours of the front bumper cover. This change improved laminar flow (allowing the air to stay attached to the part longer). The marketing claims were met, but more importantly, it marked the largest drag reduction from model to model in the company’s history.