The Chinese philosophy of yin and yang, describes how apparently opposite or contrary forces are actually complementary. Just as a shadow cannot exist without the sun, a complex mid-high volume plastic part cannot exist without a mold.
A part or parts are designed, and then a mold is required to make said part(s) in production. All three, part designer, mold shop, and molder, will have to work in concert with each other to arrive at a successful conclusion in both a timely and economical fashion. Communication is key, so having the mold shop AND the molder under the same roof makes a great deal of sense. Yet they are a true yin and yang relationship.
The mold shop designs one, unitary purpose, sole item of hard metal/steel with multiple parts to exacting dimensions, and then rarely makes another. The plastics molder uses that mold but makes volumes and volumes of parts, that can be malleable, can have processing effects on dimensions that can require “flexible” dimensioning schemes, and continues to repeat making that part for the life cycle of the product. These are two very different manufacturing scenarios, (yin and yang) that must communicate for you to succeed at getting your mold AND your molded part(s).
It makes the most sense to have them under the same roof, but managing two polar opposite business settings require a deft touch and openness to the different concerns and issues. Advanced engineering skills are necessary, but also the business mindset to recognize the dichotomy of their two operations but still make them gel.
Yin and yang can be thought of as complementary (rather than opposing) forces that interact to form a dynamic system in which the whole is greater than the assembled parts. When evaluating your supply chain, what is the relationship you envision and see between mold shop and molder? Are they under one roof and do that well?