Toleransproblem vid produktion och montering av prefabricerade betongelement
Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesis
The idea with constructions made out of prefabricated elements is that it should be quick and easy to build as the demands for lower production costs, increased profitability and shorter production times are constantly increasing. High accuracy in measurements and well-balanced tolerances is required to achieve this. The fact that the concrete-elements doesn’t fit and that damage occurs during assembly is a highly topical issue even though we now have methods and systems that make this high-intensity construction possible. Through this report we want to highlight the problems that cause the dimensional and tolerance problems and give suggestions on how to come to terms with these. The aim is that the conclusions in this report in the long run hopefully will lead to time and cost efficiency.
The fact that dimension and tolerance errors occur isn’t news for the industry. Nor that the cost to fix them greatly increases the farther forward in the product chain one goes. Where in the production- chain do they occur and what causes them? Where in the production-chain are they corrected? How’s the knowledge regarding dimensions and tolerances of those that are working in production at the factory and at the construction site? When an error is detected, is a deviation report always written? What’s the opinion regarding the deviation management system?
The work will begin with a literature study that will keep on going throughout the whole time of the report. The literature study will in detail explain what the terms dimension and tolerance mean, how they are used, the different types of combinations that exist and how to calculate them. Furthermore, the literature study will also examine the results of studies and surveys made by others. Two field trips will be carried out, one at a concrete-element factory and the other one at a construction site. The purpose is to gain a greater understanding of the preconditions for the writing of this report. Three semi-structured interviews will be conducted according to a stratified selection. The plant manager, assembly manager and the assembly foreman will be interviewed. The questionnaire study is a group survey with cluster selection. The survey will be conducted by the workers on a construction site. The assembly difficulties of prefab elements that occur derives partly from drawing errors, manufacturing defects and that installation and construction site tolerances are set too stint.
The fact that installation and construction site tolerances are set too stint is probably due to customer requests. Drawing errors and carelessness in production stood out as the most likely causes to why dimension and tolerance errors occur. This is something that we think could be reduced by making more distinct drawings. We believe that drawing sheet should be easy to understand and that it sometimes might be a good idea to make more drawings with fewer measurements on each. More technical equipment was requested at the construction site. This was requested to gain access to more drawings at the assembly location and for the ability to enlarge in order to enhance clarity.
The majority of errors that were detected in the plant were also corrected there. But if there’s a rush to send an element and the defect is small they notify the assembly crew, and then they have to correct the defect at the construction site. The plant manager thinks that awareness of existing dimensions and tolerances among the factory employees are good. At the
construction site 91% of the employees thought that it would be good with an educational course about existing dimensions and. The deviation management system is something that all the interviewees basically thought was good but that the possibility of feedback and improvement could be developed. Many minor errors aren’t reported because in many cases it takes more time to write the report than to correct the error. We think it would be good if all the errors were reported so they could estimate the cost to correct them. In order to correct some recurring production errors, investments in the factory would be necessary. There’s a constant discussion about whether the cost of the investment is profitable compared to the costs of correcting the errors at the construction site.
Place, publisher, year, edition, pages
prefab, prefabricerad, betong, produktion, montering, tolerans, toleranser
IdentifiersURN: urn:nbn:se:hh:diva-26356OAI: oai:DiVA.org:hh-26356DiVA: diva2:742867