Paper Crate Assembly FAQ: Time Studies and Hidden Labour
A crate is made of board and seconds. These questions cover how to time an assembly, where the hidden labour sits, and how to change a design without losing the protection it provides.
Why is assembly labour hidden in a crate quote?
Because it is absorbed in overhead rather than quoted per crate. A quotation lists board, glue and fasteners, and the workshop's time is a rate applied to a total. When a design adds folds or a two-person step, the cost appears as overtime or as a missed delivery rather than as a line item, so the design that caused it is never compared with the design it replaced. Counting the operations and timing them puts the cost back where the decision is made.
How is a time study run?
Time ten crates with two operators, using the actual jigs and the actual sequence, and record the average, the range and any step that needed a second person. Include the handling between stations, because picking up, turning and aligning usually take longer than the operation itself. Time the first crate separately, since learning is part of the real cost when a design is new, and report the steady-state time for the specification.
The International Safe Transit Association publishes packaged-product test procedures that a crate must pass, which sets the performance floor against which an assembly simplification is judged.
Which design features cost the most time?
Two-person folds, long glue lines, and steps that require waiting for an adhesive to set. A two-person fold doubles the labour at that step and breaks the flow of a one-person station. A jig, a pre-crease or a smaller panel can remove it. Waiting is a cost too, and a hot melt that sets quickly can pay for its higher price by removing a pause. Count the steps that stop the operator, because those are the ones that decide the cycle time.
Does a simpler design still protect?
It has to be tested, because simplification can remove strength as well as time. A self-locking tab that replaces a glue point may be as strong or weaker, and only a drop and a compression test says which. Treat the simplified design as a new product and run the same route tests, then compare the assembly time and the damage rate together. A saving that increases damage is a transfer, not a saving.
ASTM International publishes compression and conditioning test methods for shipping containers, which provide the basis for comparing a simplified crate with the original under the same conditions.
What about training and learning time?
A new design has a learning curve, and the first shift is slower than the tenth. Include the learning time in the business case rather than in the steady-state figure, and plan a few days of reduced output. A design that is faster in steady state but needs a week to learn can still be the right choice for a long run, and the wrong one for a short order.
How should the workshop be involved?
Ask the people who assemble it which step they dislike most. They know where the hands wait and where the second person is needed, and they will tell you if the question is asked before the design is fixed. A design reviewed with the workshop costs a meeting and saves a redesign, and it often produces a better idea than the drawing did.
What belongs in the specification?
The number of operations, the target assembly time with the method and the number of operators, the adhesive and its setting time, the jigs required and the route test that the design must still pass. Add a time study to the first article. A crate specification that describes material and strength has described the product and not the cost.
How should a change be evaluated?
On three numbers: material cost, assembly time and damage rate. A change that improves one and worsens another is a trade, and the trade should be calculated rather than argued. A simple sheet with the three numbers for the old and new design is enough, and it is the document that lets a manager approve a change without relying on a supplier's assurance.
Record the assembly time on the product drawing, not only in a cost sheet. The drawing is what the workshop sees, and a target time printed next to the part list turns an abstract cost into a daily measure. A team that knows the target can tell you when a batch of board is cutting badly before the finished crates show it.
Compare the part count as well as the seconds. A crate with fewer components is faster, easier to store and less likely to be assembled with a piece missing, and the last of those is a quality risk that a time study does not show. The simplest design usually wins on all three.
When a new adhesive is introduced, re-time the assembly. A different open time changes the rhythm of the station, and a team that was fast with one adhesive can be slow with another. The adhesive is part of the method, and the method is what the study measures.
Finally, keep a sample crate assembled by each operator for the first week of a new design. The differences between them show where the instruction is ambiguous, and the fix is usually a mark on a panel rather than a longer instruction.
Ask for the assembly time in the quotation and compare it with your own study. A supplier that quotes a time is confident about the method; one that cannot is likely to discover the labour after the order. The comparison takes an hour and it prevents a price that rises after the first batch.
Consider the storage of the parts as part of the labour. A design with many components needs a picking area and a sequence, and a missing part stops the station. A design with fewer parts stores more compactly and is easier to kit, which reduces the time before assembly even begins.
When a crate is assembled by a team rather than one person, time the team as a unit. A step that takes four seconds for one operator can take twelve in a team if the flow is interrupted, and the team time is what the order costs. The study should match the way the workshop actually works.
Finally, record the time for each product variant. A crate that is similar in appearance can differ by a fold and therefore by a shift of output, and the variation is invisible in a single average. The variant times are what a planner needs to promise a date.
Track the assembly time per crate as a weekly metric, not only in a project. A drift upward is the first sign that a board lot is cutting badly or a jig has worn, and the metric catches it before the delivery date does. A simple average per shift is enough, plotted against the target.
When a customer asks for a design change, quote the change in assembly time as well as in material. A customer who sees that a decorative fold costs a few seconds per crate can decide whether the appearance is worth it, and the decision is better made with the number than with an opinion.